The majority of religious people (actually all, I would argue) follow their religion for purely social reasons. Intelligent people can believe in God, but no-one has ever actually come to belief in God intellectually. They may try to intellectualise it later on, but they're coming at it from an intense desire to believe for whatever reason (usually social or emotional). Intelligent people still believe in God for the same reason intelligent people still don't accept that their wife is cheating on them when it's obvious to everyone else.
We've got people on this thread boasting about how 85% of people 'believe in God.' And yet 85% of that 85% live in places where if they publicly denounced the prevailing religion, at best they'd end up ostracised from their community, and at worst, they'd end up dead. Which shows what a sham the whole thing is, based entirely on social belonging and control, and not at all on any kind of objective observations about the nature of the world.