Grass is really good at filtering/absorbing/treating stormwater so you might have to force everyone to keep their lawns lawn because the way you've got the lots graded you need that little bit of extra because it lets you make your "shit parcel" where the basin will go a little smaller and squeeze one extra house into the development.
Beyond that I think what a lot of it comes down to is that local governments are invariably run by a lot of the same kinds of busybodies that HOAs attract and the way rules are written these days the "normal permitting process" exists only to let the useful idiots think that just about everything isn't discretionary. There's always some gotcha or twistable phrase so everything goes through a special permit or variance of some sort. That opens up all sorts of off the record dealing wherein the developer agrees to throw everything and the kitchen sink into the initial HOA rules and the Karens in government make sure those things are in there before deciding how to exercise their discretionary approval.