For starters, just look at her:
That's argument enough right there.
But here's a few more reasons: She's already a fan-favorite. Her biggest role to date was in Pitch Perfect, which means that she wouldn't be coming into the Marvel universe trying to make people forget her last role. And! She'd be perfect for a character the MCU should really consider adding:
KATE BISHOP ALL THE WAY!
After Infinity Wars, Marvel is going to have a lot of choices to make, but my hope is that they'll consider bringing in the Young Avengers. And Anna Kendrick would be the perfect Kate Bishop! But just to make sure she's available when the time comes they should really lock her into a contract now...