The thing is, not everyone got the time to wade through the mass of JS frameworks available today. The intention of TodoMVC is to give you a taste of each framework, which can help you narrow it down. You can think of it as speeddating JS frameworks. It's by no means perfect and I agree that it should not be your only source, but it's a lot better than just trying out the most popular one and using that.

Disclaimer: I'm one of the devs (Sindre).