Angular 1.x was never meant to be an MVC initially. It was mainly for templating then they started adding stuff to it (services, directives, digest cycle, dependency injection...) leading to API bloat
By the time Angular 2 was released, Ember, Vue and React have devoured the market
Facebook's motto is "move fast and break stuff." I'm glad they didn't follow this when making React Fiber. I suspect they learned from Angular 2's failure.
They saw what happened with Angular and Angular 2—which Google named the same despite it being a totally different framework—and made a smart move.