Because it's built and bundled by a monopolistic company with an (at the time, maybe less now) institutional commitment to backwards compatibility forever. Winf

Because it's built and bundled by a monopolistic company with an (at the time, maybe less now) institutional commitment to backwards compatibility forever. Winforms could have been the worst thing ever written and it would still be around and maintained. See WPF (not the worst but not much loved), that will live a long time, even with Microsoft seeming to back off on forever-backwards-compatability.