C# I don’t believe was/is a common tuning for most western instruments, classical or modern.

A digital piano can transpose things to make it “easier” to play.

Cursory google search says that a sitar is traditionally tuned to something useful for c#

I’m curious if C# is one of those notes that lines up nicely with whatever crappy consumer stereos/subs were capable of reasonable reproducing in the 90s as electronic music was taking off and it stuck around as a tribal knowledge for getting more “oomph” out of your tracks.