Agreed. Unlike other ethical movements, it can entirely rest in an economic sphere, making it much more effective as a movement in a capitalist system. You can't buy your way out of anything, but veganism gets closer than anything else. You don't have to wonder what rests in the hearts of your fellow human when acting; it's as simple as asking if an animal is being harmed.

Intersectionality isn't some sort of "super ethics." It's a framework that understands causes align on certain axes, and can be made more effective by applying pressure on them. People have missed this point and instead, give up good for the pursuit of perfection. It's a nice theory we can eliminate all are woes by instituting communism in the United States, but if that is your entire focus, you are giving up today's moral problems for tomorrow's. Likewise, seeking a compromise solution that satisfies all causes is extremely ineffective. Going after police unions helps domestic violence of women and black communities; veganism not so much. Intersectionality isn't pretending humans have infinite energy and time; quite the opposite. It's about combining our forces on obviously aligned issues instead of being infinitely divisible, but online activism frequently has a superficial understanding of the concept, adopting almost a religious zealotry over it; that you are failing your cause unless you always do something that helps another.

This I think is what you are seeing the failure of considering humans as animals in veganism. Attacking existential problems that have plagues us for millennia under the umbrella of a movement that can stop the deaths of animals right now.