Then wouldn't he be promoting it?

The interview didn't sound as bad as y'all made him out to be. He's at least apologetic that he doesn't know the girls' names (and even then it sounded like he only met them for a few minutes and the rest he didn't even see at all because they were late). And he's a rapper. They usually don't mention their collaborations given how much they collaborate.

Oh, I'm sure Tyga would rather have worked with them as well

It makes sense for him not to tweet heavily about the song. Most of the people following him are hip hop fans who could care less about Fifth Harmony.

It probably just sucks to have your biggest hit being a feature on a song that was once HIS own, for some girl group he probably hadn't heard of prior to this song.