That's not the reason why anyone builds a design system. Companies need a design system so their own developers can build consistent UIs easily. If you've ever seen the output of a company that has lots of teams and no consistent way of building UIs you'd be horrified. Their products are a mess, and the UX is terrible because each app (or part of an app) works differently depending on which team built it. A design system is an attempt to solve that problem.

Most companies have no reason to release their design system to the public. When a company does that it's usually dev rel, or just plain marketing.