I think it's just a side effect of creators securing paying bases, regular quick releases are important when trying to get new people to play and support you, but after having a solid foundation, it's possible to think more of releasing quality content in bigger chunks than releasing more stuff as fast as you can. From a developer perspective, I would say bigger updates make more sense, there's less pressure to cram sexy stuff just to have something in an update, the possibility of adding stuff to all branches (when they exist), longer scenes, more time to debug and polish content, etc.
There's also a factor of growing skill and expectations, as the creators get better, they are expected to make more complex stuff, longer scenes with more renders, shiny new mechanics, etc, and that costs time.
As a side note regarding the team working in porn games, I think that's not the best idea for all games, sometimes you can get a few people to work together in a project, most of the time these projects are one man teams making their vision come true, adding more people would add complications and possible conflicts to the mix.