So, there are few different ways to frame the OP question. One question is simply what motivates people to accept theism and religion. That is where things like fear of death and uncertainty, and social conditioning come into play. But even though these fears and social pressures can vary between people, these are often just as much in play for many atheist, who despite these factors wind up rejecting the religion they were socialized with. Given the same degree of emotional biases and same social pressures, one person can still reject religion and theism while another embraces it even more strongly than their social experiences would predict (e.g., the person who becomes more fundamentalist than their barely practicing parents). So that raises the question of what factors about the person determine how they respond to natural human biases/emotions and social pressures that favor religion.
I think their are differences in intellectual values that allow some people to engage in more willful self delusion. I think very few people in modern societies lack sufficient intellect or knowledge to realize that God is a made up self serving idea that is highly implausible. Realizing this takes little more intellect that realizing it about the tooth fairy, which nearly every kid is cognitively capable of even prior to puberty.
Rather some people are more willing to put forth the effort to con themselves into believing and it doesn't bother them to be intellectually dishonest and knowingly reject rational thought when it suits them do so. In essence, they make a willful choice to be irrational and give into their emotional biases. This is why most theists will engage in rationalizations and arguments to defend their beliefs that they themselves easily see are invalid when they given about a different topic.
Another similar factor is something called "cognitive style", which is not about what one is intellectually capable of doing but rather the degree to which one tends to bother using the intellectual abilities they have versus just giving into intuitive and emotionally-based biases that typically favor a particular conclusion without having to put forth much effort. In fact, there was a study where they showed that theists are more likely than atheists to give objectively wrong answers to rather simple math problems, when the wrong answer was one that tends to come easily and intuitively to mind. For example, "Imagine that a bat and a baseball cost $1.10 in total. The bat costs $1.00 more than the ball. How much does the ball cost?” Research shows that the answer of "10 cents" comes quickly to mind for most people, both atheists and theists. However, theists are more likely to go with that initial intuition and give it as their final answer, whereas atheists are more likely to be skeptical of that intuition and put it in the effort to reason about it more analytically to reach the correct conclusion of "5 cents". The research shows that theist are not generally worse at math, but just fail to use their math skills when their is an intuitive answer that comes easily to mind. Follow-up studies showed that if you have theists think about past experiences when they were rewarded by going with the intuition, they later report being more confident in their religious beliefs. But if you have them think about experiences where their intuition about something was wrong, they become less confident.
Tom Sawyer said:
I think one of the main things is that for 90% of religious people, the fact that they're religious really doesn't matter. It's just kind of a default setting like cheering for the local sports team. Sure, you could take the time to look into the sport and analyze other teams and decide that one from two states over is actually more to your liking, but why bother when it's just so simple to cheer for the guys who wear your city's name on their jerseys? There's no particular benefit to it and the relevant and important parts of your life won't be affected at all if you bother, so there's not a need for it.
Religion is the same way. Most people see their own religion as vaguely good and it doesn't cause them any problems and there's generally no real improvement in one's life brought about by switching to Hinduism or atheism or Yogic Bouncing, so there's no need for it.
There is some truth to this, but I think it's more complicated. Rooting for your sports team doesn't entail actually believing in things that
you have no basis to think are accurate and which are rather obviously implausible and made up. Wanting my team to win is a preference not a belief. And even when sports fans believe things about sports that are emotionally biased (e.g., that pitch was a strike, my QB did not cheat by deflating footballs) there truly is no real consequence to being wrong and the disagreements are just mere, entertainment. But every theist knows that disagreements about religious beliefs are deadly serious and have major consequences. Not only are there serious real social and political consequences of disagreements, but for any sincere believer there are eternal consequences if their beliefs are wrong. Sure, there are many insincere theists whose claim to belief are just empty words, but they are far fewer than 90% of believers.
Also, it is more than that believers don't have a motive to bother to change their beliefs. Many go to lengths to defend and rationalize those beliefs, plus exert tons of pressure on their kids and others to share those beliefs, far moreso than the pressure to root for the local sports team. That shows that they do think their lives would be different (and worse) if they changed their beliefs, rather than it just being a passive indifference.
What you are describing seems like it would only apply to those who really give no thought or weight to religious ideas in their life or political choices, because they really don't believe in a meaningful psychological sense. In the US, I think that would be closer to maybe 40% than 90% (though higher in Canada and other Western countries).
