Because if they ever make it work, it's a huge potential market. If you're the only company in the world who can use the "I Can't Believe It's Not Steak" trademark and everyone knows it lets them get everything they like about eating steak as often as they like, you are going to be a very rich person.
Why does vegan food try to pretend to be meat? Why not just embrace what it actually is?
Because if they ever make it work, it's a huge potential market. If you're the only company in the world who can use the "I Can't Believe It's Not Steak" trademark and everyone knows it lets them get everything they like about eating steak as often as they like, you are going to be a very rich person.