[XorNot]

You also have to do other things like not break General Relativity.

Which MOND does: it creates huge problems fitting into GR.

Whereas dark matter as just regular mass that interacts poorly by other means does not.

[jampekka]

There are modified gravity theories that are compatible/extensions to GR, e.g the f(R) gravity theories.

Nobody probably believes MOND as such is some fundamental theory, rather as a "theory" it's sort of a stepping stone. Also MOND is used often interchangeably (and confusingly) with modified gravity theories in general.