Missing cast members

Why is it that kelly and stella almost always are separated lately?

I mean like, kelly is off doing xyz with OFI or whatever and hes gone for a few episodes then stella is so happy to have him back only for her to leave for a few episodes…

I wonder if it’s a budget issue? Like I noticed on PD they decided to showcase a couple of the detectives each episode but rarely had the whole gang together for a couple of seasons. I read something about they were given budget cuts and that was a result? But if everyone is still considered series regular then they’re still being paid…

Idk, anyone have any answers/thoughts about this? Or am I crazy lol