When you get "black bean burgers" they usually have a bunch of other stuff in them which reduces the protein. Combine with a bun and you get a lot of calories without much protein.

Beyond/impossible are not great, but they are better.

A few fast casual places like Chipotle do have pretty good bean options.

But your friendly neighborhood restaurant? Probably you can get a salad or a Portobello sandwich or some pasta or a black bean burger. In relation to those, the packaged burgers provide a reliable source of protein.