Because C standard library isn't part of the OS.

Outside UNIX, the C standard library is a responsibility of the C compiler vendor, not the OS.

Nowadays Windows might seem the odd one, however 30 years ago the operating system was more diverse.

You will also find similar issues on dynamic libraries in mainframes/micros from IBM and Unisys, still being sold.

Yeah I know the reasons for this, I'm just saying it's not usual coming from currently dominant unix-like systems.