USB dongles are popular because the mouse is paired with the dongle. This comes handy in a number of use-cases (servicing a different computer, hot-desk office, non tech-inclined people).

It is true though that USB interference for wireless dongles is an annoying reality. My Logitech Unifying dongle has issues whenever I copy files over USB. I'm not sure if later revisions or their Bolt dongles have improved on that.