The player base has been steadily increasing for years on the old school side whereas the RS3 has been slowly dying.

https://www.misplaceditems.com/rs_tools/graph/?display=avg&interval=week&total=1

I am curious how much of their revenue is propped up by whales on the RS3 side

Stardew Valley used to be published under Chucklefish. Concerned Ape separated and self published after some concerns about Chucklefish ethics.

I can see how they may have connected the Chucklefish logo from there to this game.