If make supplied it's own shell language, a simplified one, then everything would be fantastic.
For one thing, cross platform builds would be much easier to get working as there would be no issue about "is the default shell bash or ash or sh or dash or ksh or whatever" and on Windows there would be no need to use cygwin.
The other thing is there would not need to be such a huge clash between the way expansion works in shells versus make which is very confusing when you combine the two.