The Tesla superchargers are for Tesla's only and are along the Interstates about 140 miles apart . They are put in by Tesla and if you have a Model S or X you get free charging from them . If you buy a Model 3 you don't, but you can buy time.
Free? Like the $30,000 worth of government subsidies (read "taxpayer money") that Elon Musk gets for every Tesla sold? If this was taken away, he would actually be losing over $14,000 per vehicle and Tesla would implode almost immediately. SOMEONE is paying for the electricity to recharge these cars, and my guess, is that it is WE, the taxpayers.