Approximately 0% of terminal programs use control-c as copy. Conventions depend on context.
"Control-C sends SIGINT" has been a standard for longer than "Control-C means copy".
"Control-C sends SIGINT" has been a standard for longer than "Control-C means copy".
I blame Microsoft.
(I still have a few Windows apps we use at work that use these standards; good to know they actually were a standard.)