Tech is full of examples of 'successor' technologies, that were aiming to provide a clean rewrite without legacy, which then got bogged down with supporting a bunch of corner cases and accumulated their own share of cruft and could be no longer be considered a cleaner alternative. All the while the majority of the userbase being stuck on the old platform because the new one is buggy and doesn't offer anything tangibly better.

Vulkan, various node replacements come to mind.

Wayland at this point has existed almost as long as X11, longer if you only count the Linux years, yet its still not quite there.