"users" of Makefiles are actually developers, not secretaries, pensioners or architects. They should at least understand tradeoffs and choose accordingly.

Developers are used to not using spaces: oneStupidClass or AnotherStillStupidClass or others_do_it_like_this or bIhatehungariannotation or daxpy .

As you can see it is not that bad and it has been a widely used practice for decades.

Since you are comparing specifically to windows land, perhaps it is their focus on using spaces in file names that made them always be worst than unix like systems in terms of stability, sequrity or performance.