Playing an emulator requires you to grab the keys from your purchased switch, and dump your games. I’m not going to pretend that a lot of people don’t do this, but this is how it’s recommended to use the emulator.
Even of those who don't, some of them may still have paid for the game they are downloading. Dumping the keys/games from your Switch requires hacking it, and some people are hesitant about doing that (you might brick your Switch, or Nintendo might ban it from their online services.) Or, you might only own a recent revision–which are far more difficult to hack than the first revisions were.
