>On the one hand I feel like this is just former frat dudes hyping up frat life as they normally tend to, over glorifying every aspect of it. >

As someone who's always hated frats and sororities but had several close friends in the latter, I can confirm that they do have this much sex and they do still over hype it. The vast majority of the sex happens between fraternity and sorority members, because that's the #1 purpose of them. Some of it is straight up non-consensual, and most of it is problematic at best and stems from peer pressure.

>One, from the opposite sex perspective sorority girls are also often viewed as more attractive. >

Pretty much only by frat guys, because they know they will have an easier time finding someone to sleep with (or tricking/pressuring them into it).

>Two, people in greek life are usually well-off financially. Frats and Sororities are a way that people literally pay to build a social circle and have friends. >

This is all of it. Well off students who are used to being seen as elite pay to make sure they get the experience that bolsters that view. We have to remember we're talking about teenagers here, so sex = clout. The few people that aren't well off have been conditioned by their families or friends to believe they'll only be accepted if they join a frat/sorority, thus making them extra susceptible to bullying/peer pressure/sex they normally might not choose to have.