You can't because the only people remaining (or the overwhelming majority) in those communities are people who are actually religious and take the whole thing pretty seriously.

In the past (of course it depended on the exact time and place) occasionally going to church even if many treated it mostly as a formality was the default for most people. Even if you didn't, chances are that you couldn't ignore it entirely because you still had some links to the community surrounding it through family members, various organizations, events etc.

What you’re describing is basically Unitarianism.

Religion is a meta-organism that uses minds as it’s substrate.

Just like ordinary organisms, it undergoes mutations and evolution - its characteristics are seldomly 'designed'.

Without community to keep it alive, it will die out. So religions that include practices to tie communities together are at an evolutionary advantage.