Because atheism was the official ideology of the soviet union, the only place (maybe to eastern bloc countries) where we can get an idea of what the absence of religion creates.
In other words, tehre was a formal program of atheist education in the school system.
I dont understand your point about Gates or Buffet
Atheism was
not the formal ideology of the Soviet Union, Communism was.
Atheism cannot be the formal ideology of anything-atheism simply means lack of belief in god\s.
If atheism is a formal ideology\religion then is baldness a hair color? Is not collecting stamps a hobby?
A part of the Communist ideology was enforced atheism, there were various other components.
Atheism by itself has no ideology apart from non belief in a deity\deities, an atheist can be sexist, racist, egalitarian, capitalist(hence my example about billionaire non believers)animal lover\animal hater, nudist\preferring modesty-he\she can pretty much believe anything apart from the disbelief in God.
Islam is a religion, a formal ideology, it includes strict monotheism, but also other rules & regulations like abstaining from pork, despising idolaters, jizya etc. However, deism includes belief in god\s, but no rules apart from that, a deist can belief whatever he\she chooses-they don't have a rule book of deism.
Same for other religious or political ideologies-but atheism is simply disbelief.