No, it's more than inertia. Think about lobbies instead. Sure, the whole picture is rather complicate, and my purpose wasn't to fully analyze it. I was mostly focusing on the bottom view, i.e. most people without any specific economical/political interest in supporting religion. For them it's mostly inertia.

At the higher levels, for sure, there's an intricate web of relationships that has to be balanced, and religion is still a powerful instrument for some power groups.