Why did Ezekiel say that God gave laws to the people that were not good?

Ezekiel was writing at a time of transition between polytheism and monotheism. The Bible pictures the Israelite religion as pure, monotheistic and different from the false worship of all other nations and peoples. Lester L. Grabbe says in Ancient Israel, page 150, this is the surface image, at least. We now know that during the early monarchy (prior to 722 BCE), the nations of Israel and Judah had been polytheistic, although undoubtedly Yahweh (YHWH) was the chief, national God. Mark S. Smith says in The Early History of God, page 11, that monotheism (as we understand Judaism today) was ultimately a product of the Exile; but the Babylonian capture of Jerusalem is only reported a little later, in Ezekiel chapter 21.

Josiah, king of Judah from 641 to 609 BCE, introduced the Deuteronomistic reforms intended to usher in the monotheist worship of Yahweh. The untimely death of Josiah ended this, with the partial restoration of polytheism under Josiah’s successors (see 2 Kings 23:31,37). Now Ezekiel, who became a a priest to Yahweh during the time of Josiah, blames every misfortune that befalls Jerusalem, on the affront caused to Yahweh by the open worship of other gods. So it is in this context that he is writing of the anger of God (Yahweh) towards the idolatrous people "Because they had not executed my judgments, but had despised my statutes, and had polluted my sabbaths, and their eyes were after their fathers' idols." His reference to "their fathers' idols" shows that Ezekiel knew that the ancestors had used idols for worship, but for the present generation this was wrong.

You get the picture of pious Jews, trying to live righteously, following the law, 
only they have been tricked by God himself.

The picture should be clearer now. Ezekiel was committed to Yahweh as the only God of the Jews, and was exerting his influence to guide them back to the vision of King Josiah and his Deuteronomistic reforms. According to the dominant Documentary Hypothesis, it is unlikely that the Book of Leviticus had been written at this stage.

Great question!

First let's take in the whole chapter. In chapter 20 God is speaking to Ezekiel of the story of how he chose Israel. God tells how gave them good rules, to take away the idols of the other nations from their midst and they would continually disobey. Read Exodus and see how many times they fudge up.

"*We should notice this, again, about the whole sacrificial system. Originally, God did not demand animal sacrifice (see Jeremiah 7:22). The point behind the sacrificial system was, at least in large part, connected with the false worship of the people groups around them. The animals that were to be sacrificed were those animals most used in pagan worship as depictions of gods. The bull god, Apus, is a very popular one in many parts of the ancient Middle East. Since the people insisted on offering animal sacrifices, God commands that they slay the very animals which are worshiped as gods by their neighbors. Every sacrifice is not only a costly act of real dedication to God (since land, children, and animals are the three primary forms of wealth in antiquity), but it is also a rejection of idolatry/false worship. Because of the golden calf incident, the High Priest in particular will have to sacrifice the same animal every time he comes into the Most Holy Place (or Holy of Hollies) in the tabernacle (and later Temple). Later on, especially through prophets like Ezekiel and Isaiah, God will repeatedly tell the people that the point of the sacrifices and the bloodshed involved, is NOT because He needs it (as if He is "hungry" like the other pagan gods), but because they do. They need to reject false worship. When they simply go through the motions, then go off to worship other gods, too, God tells them that He hates their sacrifices. See Isaiah 1:11ff. for example.* " - Dr. Fodor of JWCC

God's covenant- His kinship with Israel as His firstborn son (His priestly people) among the nations is one important theme throughout the Scripture which is connected, however, with the change in God's directions to Israel, especially in how they were to interact with the various people groups in the Land.

"The pagan occupants of the Land were originally to be converted. When it became clear that Israel was too weak to do this without being converted to the religions of the pagan peoples rather than visa versa), the command was changed. God's original command to convert these peoples, but not to intermarry with them (since such intermarriage had corrupted God's people before (beginning in Genesis (Plan A, is found in Exodus 19, with their call to be a priestly people to the rest of the nations, and, in fact, they had already come up out of Egypt a "mixed multitude," that is with some of the Egyptians joining them in following Yahweh, Ex. 12:38). Plan B was for them to drive these people out. See Numbers 33:50-56. They were to drive out all the pagan inhabitants of the land, and they were to keep none of the defeated peoples' property or animals for themselves, lest they fall into the idolatry endemic in these pagan cities (Numbers 33:51-53). When the absolute failure of Israel to pass any of the tests of trust and obedience toward God made it clear that even this would not work, a final plan- Plan C, if you will, was given: for these peoples to be essentially destroyed. This was a final concession, just before Moses' death, to the utter weakness and faithlessness of the Israelites. They were to follow what was known as "cherem" (or "herem" ) warfare. The approach of herem was thoroughly concessionary- a result of Israel's great spiritual and moral weakness. Note the contrast between the original legislation of Exodus 23:23-32 (forbidding marriage or other covenants with Canaanites) and the Deuteronomic commands (Deut. 20:16-17) calling for the complete destruction of all peoples who do not flee before Israel. The concessionary character is picked up by Jesus in His Sermon on the Mount (Matthew 5:43-44). See verses 5:17-48 playing out this theme in detail. The whole Deuteronomic code has the character of a concessionary law. This is what "Deuteronomy" means, as we have seen. Not all people groups were listed as being under the ban, and even some of those who were included were spared when they showed evidence of wanting to follow Yahweh, including some famous foreign women like Rahab and Ruth. The Gibeonites became kin, and accepted Yahweh as part of this. Though this involved deception, it does give hints at what should have happened to all the groups originally: that they should have voluntarily joined Israel. Later, God even says this about this concessionary code:

"I also gave them statutes that were not good and ordinances by which they could not live" (Ezekiel 20:25).

But this was a specific tragic necessity directly allowed by God." - Dr. Fodor's notes on the covenant law (he is a teacher at John Wood Community College)

Also in Amos 5:21

“I hate, I despise your feasts, and I take no delight in your solemn assemblies. 22 Even though you offer me your burnt offerings and grain offerings, I will not accept them; and the peace offerings of your fattened animals, I will not look upon them. 23 Take away from me the noise of your songs; to the melody of your harps I will not listen. 24 But let justice roll down like waters, and righteousness like an ever-flowing stream.

God cares more about the heart that craves justice and righteousness than traditions and rites.