[2020] How do people sell a vast amount of LOL accounts?

A large portion of sold accounts are accounts that have been compromised from their original owners and then sold. When you're buying an account, not only are you breaking the ToS (and we can identify if an account has changed hands), you're also likely buying an account off someone whose account was stolen from them.

the account won't get banned

https://i.imgur.com/FXLThSZ.jpeg

I can't confirm or deny anything particular about how we ban bots, but the IFS will only give you a notification if your report was the thing that resulted in a ban. That's usually not going to be the case for botting for... complicated reasons.

That doesn't mean accounts don't get banned.