I could be off base here, but I actually think that a girl being mid can sometimes help with her thot sales.
If a guy is paying that amount, it probably goes deeper than him just thinking she's hot. He is probably emotionally attached and is fantasizing about her being his gf or something similar.
For a lonely simp, the fantasy of dating an attainable 6/10 is much more realistic than dating a supermodel, so paying for a girl like her means they can more easily indulge in the fantasy without feeling too ridiculous about it.