It's because Tesla's navigation automatically adds charging stops to the route. Also you add billing info when you set up your Tesla account (which the car is tied to) so you don't do anything besides plug in. While you're driving you can see on your car's screen how busy nearby chargers are, whether any stalls are out of commission (an extremely rare occurrence), and what the maximum charging rate is.

I've tried 3rd party chargers a few times and gave up on them. They're often broken or extremely slow. They usually require installing some app, and you don't know whether they're occupied or not until you get there. In contrast, Tesla's chargers are a consistently good experience. Without them, I'd simply never use my EV for road trips.