The business apps I work on don't benefit from SSR (having to write components that can render server-side is friction without payoff), and I already have a client-side router that supports nesting.
I'm still using https://github.com/TehShrike/abstract-state-router which I wrote years ago after thinking "ui-router is great, but I need a version that can keep using no matter what component library I want to use in the future"