I don’t think anyone is suggesting Haiku to compete against windows or macOS. It seems to be more of a hobby play than anything else. The real company failed trying to commercialize this — why would a design from the 90s be commercially viable now when the main selling features are standard, and all the innovation is on phones anyway?
And how can one even make money selling an OS these days? They may have a small marketshare from techies wanting it for fun but turning this into an actual business I would think would be very difficult these days.
Yes, absolutely, spot on.
But an OS does not exist on it's own. I'm afraid it will all be for naught unless you (or someone) has a viable business model to push the surrounding ecosystem forward.