I think they're afraid that one brand will be so much more successful that the other goes away. Each brand has different flavor, texture, and nutritional profiles so if any of those are particularly important to you then it's hard to make do with one of the other options.
For example, both Beyond Meat and Quorn sell meatless "beef" crumbles. Each has a noticeably different flavor and fairly different nutrition (The Quorn has significantly fewer calories, but less protein for example). I would be sad if either one went out of business because I use them differently.
It's still such a niche market that expanding it right now is the best thing for all the players. Beyond Meat revenue is $33m compared to say Tyson at $33b. The veggie meat market is also a lot less homogenic than meats since everyone makes their own proprietary blends from thousands of possible ingredients. Compared to say cheap chicken where it's impossible to tell brands apart.
For example, both Beyond Meat and Quorn sell meatless "beef" crumbles. Each has a noticeably different flavor and fairly different nutrition (The Quorn has significantly fewer calories, but less protein for example). I would be sad if either one went out of business because I use them differently.