I nearly went to a private party then decided it wasn't for me for reasons that I don't need to repeat here.
But my potential party differs from your experience as it was a fixed entrance fee then sex with all the girls present.
At the other end I have been to strip clubs where you pay £20 for a five minute no touching lapdance. 5 of those and you're into triple figures.
I think the party you are describing is halfway between, they treat you like a very elite strip club where they are earning money like a stripper but because of the private nature, are allowed to do extras.
If the guys are lining up they must have money to burn, these girls could be making over 1000 a night.
Conclusion : They are preying on guys who don't know there is a better way. I wasted money in strip joints cos I knew no better way. What you describe is no different