He bought a house in LA because it was the thing to do at the time because he knew he’d be spending a lot of time in LA shooting PIC (he even said as much in an interview IIRC). He has a few properties that enable him to always pretty much live where his main career events tend to take place, it made sense to add LA to that mix. This is nothing out of the ordinary. And yeah it’s also true that PIC is the only Trek series that’s shot in California mostly because he insisted on it. So, generally speaking, him buying a house in LA means very little in the context of how many seasons PIC will have. He just likes to be comfortable. 
