these are full time farmers, they aren't sitting around at home with 2 phones waiting for teenagers to pay retail price between fortnite matches. Instead they sold bulk on average for $660 / LB this last year, so ~ $250-330 per outdoor plant. MOST of that average is indoor high grade, so this can be seen as a ceiling on outdoor plant economics.
So your napkin math that "you can get a lot more than $500 off a single plant" appears to overly enthusiastic.