If I bought 100 tickets, sold 20 of them at 10x the value I paid for them, and then ate the rest as a loss, I'm still making a tidy profit, and the artist/venue/etc. still make the same amount of money as if 100 individuals bought them and attended, but there are now 80 fewer people in the audience (edited to add: and potentially 80 people who could have afforded the original price but not the absurd upsell).

I don't have the data to say whether this happens or not (edited to add: and the numbers are obviously made up), but the logic is perfectly sound; nothing would stop it from happening today.