Ctrl+C is a method of generating a standard ASCII character which has meant "ETX" (end of text, sometimes "interrupt") for many decades.
Other control chars are useful too. In addition to C, I use S, Q, D, Z, V, O, N, I, G, H, M, L, J, Y, A, E, K, W ... probably others ... fairly regularly.
So in the early 1980s, along comes MacOS which needs keyboard shortcuts for GUI actions. What does Apple do? They add a key to the keyboard, an Alt or Meta equivalent called "Command". OK, awesome.
Then Windows comes along. Microsoft says "eh, who cares let's break it all", (or more charitably "we don't control the hardware and can't add a key, so let's break it all") and reuses Ctrl+C for copy. Et cetera.
Then Linux desktop environments come along and say "well people really like Windows...we don't, but most people who might try our DE probably do, so let's borrow the bad ideas from Windows instead of the good ideas from Unix or MacOS. Let's use Ctrl+C for copy! But also the command line is kind of important on Linux, so let's screw everything up and use Ctrl+Shift+C for copy in the terminal only because who cares about usability and UX consistency? Not us!"
That was 25 years ago. Nothing has improved since then. Alas.