Why is it usually easier to do things the wrong or unethical way than to do things the right way?

Unethical act is a personal gain, and a short cut in life; that's why it is easier to choose wrong over right. At my job, Maybell painted Theresa as an uncooperative co-worker to the supervisor for the supervisor to favor her instead. To lie on Theresa, was like looking down and counting the few pennies on the floor, easy to do. But to complement Theresa to the supervisor, it would have been like to bend down to pick up those pennies off the floor, harder and more painful to do. Unethical as wrong behavior is to please or satisfied one's own intension. While ethical or right behavior is to benefit or uplift another person's life.

Because adding arbitrary external constraints on any task makes it more difficult. Doing it ethically is harder, doing it standing on your head is harder, doing it in multiple languages is harder. Automatic property of the world.

God allows temptations like this because if it didn't require effort to do what is right, if it was always easy, then we would always do what is right out of simple expediency and never actually learn to live by faith.

OK, to really answer this, I need to define what "the ethical way" means. My answer here is going to be based on this:

Ethics, Defined

Matthew 22:36-40 NIV
“Teacher, which is the greatest commandment in the Law?”

Jesus replied: “‘Love the Lord your God with all your heart and with all your soul and with all your mind.’ This is the first and greatest commandment. And the second is like it: ‘Love your neighbor as yourself.’ All the Law and the Prophets hang on these two commandments.”

Essentially, if you love God above yourself and love other people above yourself, you're following God's commandments, and therefore, acting morally.

Anything that would be considered "unethical" would go against one or both of these commands.

_{Note that this is not the best definition, sociologically speaking, but it will suffice.}

Why do something Unethical?

Next we need to determine motivation for doing anything unethical at all.

Based on our definition, anything that is not done with (a) love toward God or (b) love toward someone else, would be unethical. Lying for your own benefit would be a good example of this. Manipulating someone towards your own gain is another example.

This seems to show that any action chosen that does not show love toward God or others would be unethical. Also, I'd put forth that we won't perform these actions unless they benefit us.

So the motive to do something unethical is so that it may benefit us (either in the short term or the long term).

Making the choice

When we come to a decision that has either an ethical choice or an unethical choice. The ethical choice is going to be one that tends to benefit others rather than ourselves.

Because of this, it makes it difficult to choose the ethical road when there's no motivation for choosing the ethical path over the unethical path. Oftentimes, the "correct" choice is made due to social coercion or guilt. But lacking these external forces, most people will, given the option, choose the thing that benefits them rather than something that does not benefit themselves.

Summary

We chose the unethical/immoral path because it is the path that has the most obvious and most personal gain. It often appears "easier" to chose this path because the personal gain of the unethical choice is such an large positive compared to the personal sacrifice of the ethical choice.

Since we see gain towards the unethical and sacrifice towards the ethical, we are immediately, automatically drawn towards the unethical choice (making it appear "easier").

It's only easier at first to do the wrong thing; but consequences follow and make the way more difficult afterwards.

Proverbs has a lot to say about wisdom and not going the easy, enticing way.

There is a way that seems right to a man, 
but in the end it leads to death. (Prov. 14:12).

and

In the paths of the wicked lie thorns and snares, 
but he who guards his soul stays far from them." (Prov. 22:5)

By contrast,

The path of the righteous is like the first gleam of dawn, 
shining ever brighter till the full light of day. (Prov. 4:18).

As to why it is easier for us to do the wrong thing, Paul speaks of the death that reigns over all mankind because of the sinful nature we inherited from Adam:

...sin came into the world through one man, and death through sin, 
and so death spread to all men because all sinned (Romans 5:12)

Our inherited propensity to sin makes it harder to do the right thing.