Will most people go the three lower dimensions (hell, animal womb, ghost realm)?

This doesn’t make sense to me because majority of humans though imperfect are ethical and moral. How true is this? How strict should we live our lives so that we can be reborn to a higher dimension?

Just do some quick math and you'll see it all makes sense, although it'd be a bit depressing to face this truth. So, assuming every sentient being gets a fair and equal chance for rebirths in any realm, just counting the total number of mammals in this world, there're ~ 130 billions. The number of humans in this world ~ 7.8 billions. So every mammal sentient being would have a 7.8 / ( 130 - 7.8 ) odds of rebirth into the human realm. Now that's just mammals, start factoring in every animal species, the hungry ghosts, the hell-dwellers, etc. and you'll see that that blind turtle simile the Buddha taught in SN 56.48 was not far-fetched at all. So, it's no longer a question about whether it's true, it's a question of whether you're strong, brave, and wise enough to face it in order to solve it.

This is a very intersting question and a hard reality. What makes you think people actually are ethical and moral? Most of people have huge attachments, envy, and are easily dragged into evil conducts. For exemple, try having a beautiful girlfriend/boyfriend, and see how many people will try to flirt with him/her despite knowing you are in a couple. Also witness jealousy around you.

Look at the world history. Does it seems peaceful? I think there is a false assumption in your question. Since most people gravitate around greed, envy, selfishness, ignorance, they are doomed to go down instead of going up in the long term (hundred of life cycles as someone mentionned)

Yes, and just something to be trusted if told by the Awakened one and or One who knows and sees. If it happens that someone without virtues and morals equal of the Noble ones gains birth under humans, he/she nevertheless experiances a low realm equal life like an animal, ghost,... Just observe the different between animals and humans in how far they are different.

In Buddhism, the 'human' realm does not always refer to something biological. The word 'human' ('manussa') in the Pali language means 'high minded'. For example, AN 6.39 says:

Bhikkhus, a god, a human or any other good state would not be evident from actions born of greed, hate and delusion. Yet, bhikkhus, from actions born of greed, hate and delusion a hellish being, an animal birth a ghostly birth or some other bad state would be evident.

It appears the Pansu Suttas SN 56.102-131 are about what happens when the Four Noble Truths are realised and when the Four Noble Truths are not realised. The sutta quoted in the question is only an excerpt. The complete sutta is:

Few are the beings who, on passing away from the human realm, are reborn among devas. Far more are the beings who, on passing away from the human realm, are reborn in hell... in the animal womb... in the domain of the hungry ghosts

Why is that?

It’s because they haven’t seen the four noble truths.

https://suttacentral.net/sn56.131/en/sujato

The message of the Pansu Suttas appears the same as the message of the Lonaphala Sutta. The message of the Pansu Suttas appears to be when a non-Arahant enlightened person who has realised the Four Noble Truths falls away (cutā) from being human, such as if they are unmindful and perform an unmindful skillful action, due to realising the Four Noble Truths, they won't fall into the lower realms because they realise there is no self that did the unmindful unskilful action. Instead, they know the doer of the unskilful action was the element of ignorance. Therefore, their human status/coming-to-be (paccājāyanti) is not lost.

The Pansu Suttas can be contrasted with ordinary suttas about kamma, which are about the ordinary outcomes that follow from (upapajjati) various acts of kamma (actions).

It is important to note, in the ordinary suttas about kamma, proceeding to (upapajjati) 'heaven' ('a happy state') due to a skilful action is not permanent. 'Heaven' is not permanent in Buddhism.

In summary:

1. The Pansu Suttas SN 56.102-131 appear to be about, due to realising the Four Noble Truths, how the human or godly state (paccājāyanti) does not change significantly despite unmindfully falling away temporarily from that state.

2. The ordinary suttas about ordinary kamma are about the ordinary outcomes that follow from (upapajjati) various acts of kamma (actions).

Note: The word two Pali words 'paccājāyanti' & 'upapajjati' commonly translated as 'reborn' are different. The word 'upapajjati' means 'to proceed closely to the former' (for example, from performing an action causing pain, one proceeds to a painful state). The 'paccājāyanti' appears to refer to the attainment of a realm status.