Unfortunately, the reality is that Microsoft has more engineers and money devoted to this problem than unity possibly can, so the official c# runtime will continue to support more platforms and being new feature and better performance at a pace that is…
…categorically not possible…
For unity to match.
So… while it’s a bitter pill to swallow, and it was done for reasons that seemed good at the time, it was the wrong choice, and that will become increasingly clear as time rolls on.
There’s what I believe is a pretty classic case of sunk cost fallacy going on with a number of current initiatives in the Unity ecosystem.
Some companies thrive under competition. Some… do not.
Likewise in what concerns iOS, Android and WebAssembly, those same engineers keep using Mono runtime, as apparently there aren't as many resources as you paint.
A good example of the resourcing problem is the ongoing tragedy of migrating the development from UWP into WinUI 3.0/AppSDK