Let me offer you a scenario: you want to build a UI web component that uses state, but you want it to be usable in both Svelte and React (with solidjs). The current situation is that it's a massive pain in the ass, because you have to move all of the state out of your code into a "driver" module that you can swap out for each of the frameworks you want to target. The entire architecture of your library is made worse (less readable/maintainable, probably less performant, harder to contribute to) in order to have a single set of UI code.

All of that goes away when the plumbing for handling state is standardized by the runtime.