"a couple generations back, makeup would be something that "adult" women wore in order to make themselves look "pretty" in order to attract a husband."

More to the point, certain types of cosmetics (especially lipstick and rouge) mimic sexual excitement. Well into the 1900s makeup was largely the province of prostitutes looking for johns, not respectable women looking for husbands. While most people have forgotten the reasons, a cultural memory that makeup is not quite respectable remains.

There have been periods where women wore cosmetics to hide scars from disease, but that is far enough back to have left our cultural memory entirely.

Personally, I dislike cosmetics because I find them less attractive than no makeup - but I don't object to girls playing with the stuff.