Copy/pasted code becomes technical debt at scale, especially if there's an unknown error in the original. Now you have 10s or 100s of variants out there, each individually tweaked and so not readily identifiable as true copy/paste repetition, all containing some variant of this subtle bug. You find out about for interface A, and fix interface A. Maybe you remember that B-C were copy/pasted versions of A and check them out and correct it there. But D-Z were all copies made by others, following your example, and you miss them.

It's not scalable, and produces severe consequences when used without care (which is most of the time, it seems).