Because in times of distress, spirituality provides comfort.
White men are not put under the same kinds of pressures and distress that black people are.
Atheism is popular in East Asia too. The more higher developed the nation, the more comfortable the people and less blatant unfairness they witness. If you live in an Arab majority country you've likely witnessed people abusing their power and have been a victim of their abuse. So naturally Islam and Islamic fundamentalism is more popular there.
In Saudi Arabia where luxuries are everywhere, the "muslims" there are Islamic in culture only. They drink, cheat on their wives, hoard wealth instead of living modestly and giving their earnings to the less fortunate. They're essentially atheists too but are in a culture where it's not okay to admit that so they go on a pilgrimage once a year, go through the motions and then go right back to sliding into DMs promising to fly sex workers to them.
A large percentage of people who claim to believe in their religion of choice actually don't. The idea that someone like Donald Trump can claim to be religious is laughable. He's not going to admit to being an atheist but you're on thar narcotic if you think a philandering racist who never forgives anyone and never gives money and power to those who have less than him represents Christian values.
