If by ”done something” you mean the devs made custom widgets have the proper ARIA roles so they’re usable for people who use a keyboard to navigate, or who need screen readers and their plethora of different navigation modes. This is usually the case when a suitable standard component does not exist or is not well supported across browsers. Hierarchical tri-state checkboxes come to mind.

The native focus system typically works just fine, but JS is needed for keyboard interactions and to set things like aria-activedescendant.