Mutants being in hiding is the best excuse. It was only Fantastic Four and Avengers in the main Marvel Universe that meant the X-men did show themselves publicly but they had to because of mutant terrorists (Magneto). Mutants are meant to be the persecuted race of the Marvel Universe, having them in hiding and people not fearing and hating them removes a large part of their character.
The problem is the hiding aspect of the MU is the Inhumans thing, their royal family are not relatable, their selective breeding and questionable past isn't one that should be pushed to the front. But Marvel are pushing them to so obviously be a replacement in the MCU for mutants, some of the lines of dialogue in SHIELD were ripped off from mutant problems it was unreal.
Spiderman is easy, just says he's around and start including him.
Hmm, pie.
