As I recall they are severly limited due to the dev team needing PS2 dev kits, which have not been manufactured for a very long time, so there are vanishingly few PS2 kits around. Even when they cut over to PC only they weren't able to de-couple things like the PlayOnline launcher, which kept everything chained to hardware that was already at least 10 years old and becomming difficult to find.

Personally I think devs wanting to move on from this game is legit. Even when I've been working on projects that I love there is a point where I just want to move on to something new.