It's just a natural side effect of software and hardware forming a symbiosis and that they cannot really be separated. New software is (or should be!) built to

It's just a natural side effect of software and hardware forming a symbiosis and that they cannot really be separated. New software is (or should be!) built to run well on existing hardware, and new hardware is built to run existing software well. Besides, subroutine call instructions were a thing long before C became mainstream and manual assembly coding ruled supreme.