It actually does. You're still supporting a browser monoculture unless you change it so radically that it makes no sense to call it a fork anymore

I mean technically, yes. However the sheer amount of LoC chromium has and the costs of actually hard forking (and properly maintaining it) makes it quite difficult. That's why right now we only have the choice of Firefox based browsers and Chromium, then hopefully a good third contender being the Ladybird browser in the future.

You could also go build a house (or even a cabin) with your own two hands, but most people typically go and buy one or pay for one to be built for them instead.