It seems likely that those with higher IQs rarely actually choose to learn about religion, and therefore they rarely know enough about it to decide to accept it.

Has anyone ever done a study to determine how many have studied theology and decided that there wasn't a God and that religion is meaningless or a hoax? Or is it only the unlearned (or dropouts) that make such pronouncements? Do any learn the answers, and then turn away, for any reason other than that their understanding never approaches that of the infinite God?

Until I read the Bible, all the religious noise, whether from those inside or outside of religion, made me quite sure I wasn't interested. You can probably tell from my word choice, I changed my mind. I started with the New Testament; I know another who started with the Old that told me she had a much harder time of it. Note also that I distinguish between the infallible ‘God’ and the ever fallible ‘religion’.

Not sure I'd even agree with your premise that believers end up poor (to be clear, I definitely don't); but to answer your question of why, it's because (the correct) religion shows you that money isn't really that important, certainly not as important as many think.

What is the point of money? An imperfect measure of the value of an object or of work performed.
To measure one's self-worth? — Then following God is able to replace an ineffective system of measure with one far more meaningful.
To achieve happiness? — Yet the studies (Pew Research in the case of these figures) are pretty clear that those who self-identify as actively religious report 8–10% higher levels of happiness (in western free world countries), despite possibly lower net worths.
To gain power and control? — Followers of God understand that the perceived power of a Musk or Bezos, while immeasurably greater than the average man, are equally infinitesimal when compared to those of God. And the lure of comparatively trivial power is… trivial.
To gain a measure of security and confidence about the future? — God's assurance lasts infinitely longer, doesn't depreciate, can't be stolen, and is far more reassuring.
To be (feel) superior to others? — The truly religious don't care. Their only disposition to others is love and caring.
To survive? — God makes sure we have what we need (the operative factor being in how one calculates need).
To enable one to help others? — Then its value is definitely not in its accumulation.

Many will call religion foolish. The heavens and the earth, and everything else, created in 6 days… talk about obvious stupidity! — Depends whether you imagine God was standing on the Earth before he created it. Or was the bodiless form, experiencing relative time in a universe without sunrises, describing sleeps? He acted (willed) for a period, and then He stopped for a period, and then the second “day” began.

We have the ‘Big Bang’ to explain our reality… what preceded the first femtosecond of that? Is there even a theory? Has someone yet guessed at what triggered the ‘Big Bang’? Genesis 1 (KJV) – “…And the spirit of God moved… And God said…”. Who can authoritatively argue that God didn't choose what followed, those mechanisms that humanity still struggles to comprehend?

The Bible — our only understanding/record of God's word — was what God was able to explain to human beings 2,000/4,000 years ago. If you explain quantum physics to a 5-year-old, even the best and the brightest, what would you expect their explanation of your teaching to amount to for others? Meanwhile being (Christian) religious is about a personal connection with an actual existing, living God; what you might get from it is likely to depend more on you than on Him.

I hope that's useful. And I hope that you find what you are looking for; you're obviously looking for something, since you bothered to ask questions.