He's basically sticking to what he knows.
When he played the game. Faith is like a consumable item; very op but once taken away, you're useless. Instead, he built up his economy and science and stacked up passives over millennium.
They an coexist like in rl. Normal ppl with faith are fine but fanatics will always exist. Fiction mirror reality. At this point, even if he did nothing, he'd still have diehard followers
So the basic idea is that "if I don't get it, neither will anyone else"? Like getting rid of potential resources other gods might have, right? But on the other hand, with the rise of sciense, faith tends to decline. Isn't it still shooting shooting himself in the foot long term?
What is Nebula trying to achieve with the creation of faithless country? Won't it be bad for him in the future?