Regardless of whether people know it exists, the world where it exists is much better than a world where it doesn't and there is only one option.

So open source doesn't work?

Alternative browsers are available based on Firefox source code. The same is true with Chromium.

Sure, but they would all cease to exist if Firefox or Chrome ceased to exist or even ceased to be worked on because they don't have the labour to keep their project going without the parent projects doing most of the work.