It's not surprising. The voice actors in this game are the highest quality I have seen in a porno. They probably get a lot of mainstream voice work offers. With more mainstream money, it is understandable that they don't want to do smut anymore. Even Oolay Tiger, who is still active in smut, has some mainstream game voicing roles and does ASMR/VTubing on the side.
I guess the same is true for the artist. I have never seen any art that comes even close to Studio Kuma's artist. He/she is probably a mainstream popular artist and Kuma paid them a lot to do smut.