Facebook is probably the single most interactive and complex application out there... it's using React. There's also more to it than just the UI portion... there's also state management, and the unidirectional workflow, that you don't get in nearly as consistent a way with Vue as say Redux.

Startups will use whatever is trendy. I'm unaware of any site the size of Walmart.com or twitter's mobile site, or Facebook that uses Vue.

Just because you disagree does not invalidate my point.