[finaard]

Problem is that you have a wide range of makes with different syntax. It has gotten better nowadays where GNU make is available pretty much everywhere, but two decades ago you'd have a range of incompatible makes on different UNIX systems, plus a bunch of incompatible makes on Windows as each compiler would come with its own make.

Assuming you can ignore Windows you'd typically end up with two makefiles (Makefile and GNUMakefile) and a bunch of includes sharing code all make variants understand.