Is the under 13 audience that large to make film makers change their movies to achieve the PG-13 rating?

Why do film makers change the content of their movies to achieve a lower mpaa rating…..to attract a younger audience to make more money? Do they really get that much more money from that younger audience? I’m curious. It doesn’t bother me if they take out a few cuss words, but when they have to change a storyline or character trait it doesn’t seem worth it. Interesting tid bit – I read on the wiki that in 1984 the violence and gore in Indiana Jones and the Temple of Doom, and Gremlins caused an uproar with parents and forced a new rating – PG-13