How are low GPAs getting into ivy leagues?

Having attended Yale, I'd need much more solid information on that than you've offered. In any case, if that graph is accurate, you'll note that very, very few people with low GPAs are getting in.

However, if someone with a GPA well below average gets in, it's because he or she is very unusual, unique, and different. The applicant would offer a special talent, a very unusual (possibly minority) background or experiences, a major accomplishment. A mediocre student who's been playing an instrument professionally, with a symphony orchestra, MIGHT have a shot, as would someone who was fabulous in the sciences and had actually published scientific research but was not very good at other subjects out of sheer lack of interest in them.

It is not true that merely being great at a sport will get you in. A coach may want a certain applicant, but Admissions staff have to be convinced that the applicant can handle the academic demands. As for wealth, well, that might work (though it often doesn't these days), and Mom and Dad had better be prepared to donate an entire building. A mere million dollars given to the Alumni Fund won't help. A phone call from a congressman won't work either. In fact it's likely to get you rejected. Admissions staff don't like that sort of thing.

If you are considered a minority applicant by Yale, you can get in with rather mediocre grades. Because of this policy, Yale was forced to introduce a pre-start summer school programme for those they have accepted but who are functionally illiterate.

Easy. You just get yourself recruited to a varsity sports team, or have your Daddy the congressman call the admissions office, or have your rich uncle donate a million dollars to the alumni club.

Minority set-asides. However, despite lots of extra help, tutoring, etc, most of them simply cannot make the grade.

They might also be underrepresented minorities who have overcome great obstacles to get the grades they did get.