I'm assuming it is because of the lower volume of alternative burgers. Looking at my supermarket, they have probably 150-200 linear feet dedicated to meat and maybe 5-10 for alternatives.

Subsidies. I'll just link my other comment from this thread.

https://news.ycombinator.com/context?id=32964298

Meat is heavily subsidized.

Because it’s newer and externalities exist?

Cows work for free.