Bingo! Religion has always been primarily about community. The shared morals and traditions are in service to making a stronger community. Its a book club on steroids. If your church is boring and asocial, nobody will want to attend.
For a great many it is also about exclusion, a purification of that community. When I lived in the US I attended several community events (BBQs, sports days and such) with friends who were "in" a local church. It was all fun until someone got wind of the new guy with a non-local accent. Then I would be set upon by people asking probing questions to nail down my religious status, questions for which there are never good answers. Once I left early as my outsider status was evidently disruptive (a "leader" was loudly trying to convert me.) I also went to a big Mormon BBQ event which was, unexpectedly, 100% different. They just accepted the presence of an outsider and didn't feel the need to even bring it up. But for some reason they did keep offering me coffee.
In that context, the rise of megachurches is a Very Bad Thing. In my experience - being from a family with multiple generations of missionaries and pastors in that tradition - these types of unaffiliated churches often tend toward cults of personality, spreading a message that is at best oblivious to the concerns of anyone outside their extremely homogeneous congregations. True hate from the pulpit is rare, but fear of others and belief in literal devils trying to drive an anti-faith agenda are quite common. People thinking one's own community is special or blessed usually goes hand in hand with an implication that The Other is defective or diabolical. While not harmful in itself, it's a stepping stone to some pretty bad places.
It's a common error to think that repressive regimes are unstintingly serious. In fact, the worst elements can never have their way without the support of a broader community, which they often nurture through recreation, religion, etc. "Church is fun" can be a good thing, but it doesn't mean those "fun" churches' effect on the body politic is a good one.
I think you're right that it stems from a need to explain the unknown, which is why with modern science we have atheism on the rise. But I don't think your pessimism is entirely warranted. A church hosting a free BBQ is not "grifting"
> A church hosting a free BBQ is not "grifting"
Having been a deacon at a church hosting state-funded food drives, I can tell you it's never completely free of strings. Even if the funding or food is supposed to be distributed without proselytizing.
They are always looking to spread their message, even if the unpleasant aspects are neatly tucked away for later. And the quiet part rarely spoken is they are seeking 10+% of your income, your volunteering time, your attention, and especially your children.
I would pause before making a causal claim. There is a correlation yes, and you see this particularly in demographics whose religions are unable to cope with the false dichotomy that is presented in front of them, so to them the only solution is to turn to atheism or agnosticism and even, ironically perhaps, scientism as we see quite prevalent today.
From our Islamic worldview, we don't see any dichotomies between scientific discoveries furthering our understanding of the world, and the existence of God. It's actually the other way around, we see the world as a sign of God, and the more we learn about it, the more we learn about His Magnificence. The Quran encourages us to learn about the world around us. After all, Islam was the main driving force that brought us the Islamic Golden Age.
If churches didn't require you to believe, maybe they'd have more attendees.
Look at "creedless" denominations over time to see how it plays out. There's no specific belief you need to hold to be a quaker for example, and as a result some quaker practices have been absorbed into other protestant churches while quakerism itself is almost dead.
It's harder to bond over sensible, obvious things that outsiders would agree with.
There's always been a tension between community bonds and reality.