All of Microsoft’s products seem like they are all trying to be everything for everyone. Instead, people want more focus. The entire experience of Windows is a mess. How many terminals does an OS need? Or settings and control panels? Or all the legacy stuff? Just start from scratch and think simple, secure, and fast…. Otherwise you get trapped and bound to endless reasons for doing stuff and no focus and end up with Windows 11.
That would be great, but starting from scratch would take away Windows' core strength: backwards compatibility. There's a lot of legacy out there that depends on all that old cruft being there. There's still critical infrastructure running on Windows XP.
MS could probably just virtualize it or containerize the old parts, but people made a lot of dumb choices back then and windows software got its tendrils into every part of the OS and so weird things can break when you try and containerize it.