because the entire MCU is expertly written and totally not based on shoehorning all the heroes for more revenue.

Probably assumed the current Avengers would be enough to stop him. They nearly did.

Because she was JV and everybody knows it 😛- really though one of my primary problems with those movies (aside from there being a new one every 33 minutes) was that they felt like they had 37 characters and references shoehorned into them, so maybe holding off on some characters is not the worst thing

And why did she turn out to be useless? It was a lazy way of introducing the character to the universe.