Literally every company I have worked for builds a component UI library. They are boring and catered specifically to the company's branding and needs.

They also grow with every feature iteration. It starts with `<Text />` and `<Button />` and then grows to include `<Toast />`, forms, modals, etc.

If the company is big enough they can make it public and get some attention but I don't see why anyone would use them for their own personal projects outside of the very limited scope of the company itself.