Colt released a semi auto copy of the M16 as the AR15 in 1963. Predates the Mini by a few years. Browning imported the first FAL rifles from Belgium in 1959. Numerous other makers started selling semi auto copies of their military rifles throughout the 60s and 70s.
Ruger "won the popularity contest" because they could be bought at K-Mart and every other gun seller as an affordable production item. They also appealed to the "traditionalists" who thought these newfangled "plastic rifles by Mattell" were junk. They won "fair and square" back then, not by default!