I can't speak for Rich Harris, but Svelte and Sveltekit were never created as part of any company. These tools were created organically.

To my knowledge, Rich is just an employee of Vercel where they pay him to work on it full time. Despite that, I believe that Svelte still aims to remain independent. I imagine that Vercel just wanted him in-house so they could keep their eye on the latest developments in the js-framework space.