Was talking with oomfs and they had mentioned that Kris playing the piano is a reminder that they're still them and I can't help but to expand upon this further.
Simple headcanon/detail - most likely, someone's probably thought of it before but I wanted to share regardless. How Kris sometimes purposefully acts obtuse and takes options we select as them literally (when they wiggle the door knob in the church and don't actually open the door, to note a specific instance), I think they intentionally gatekeep their piano playing skills from us.
Most individuals on this site can probably say they have a hobby that's just For Them. It's undeniably them. For me, it's drawing, drawing is My Thing. It's satisfy me. It's to make me happy. For Me. It's not for anybody else and I think that's piano playing for Kris.
Purposefully not knowing or not playing the piano when we make them go up to one because piano playing for them isn't for anyone else. It's theirs. As my friend said, it's reminder that Kris is still themself, but at the same time, it draws that line in the sand. One they will not allow us to cross, similar to how (especially now), they refuse to let us insult their friends through them.
They play the piano. Playing the piano is their thing, and they will not allow us to invade that.
