The Windows 11 context menu lag (and overall Windows bloat) is a product of Conway's law. Microsoft creates bloated software because it's a monopoly. So, "optimization" in this case would essentially be antitrust action.
I think the explanation isn't quite as simple as you make it seem.
It's also that you're expected to update windows whether or not they've actually improved performance. Why would microsoft prioritize that when the bulk of their sales are driven by other concerns, like enterprise sales and what some might call basic functionality (e.g. Windows Defender, when it was first released).
Hell, now they're moving to a service model and there's even less reason to court consumers directly.