It may be too bad but in the last reported cycle 830,016 applications were submitted from 53,042 applicants (an average of 16 applications per applicant) with 21,030 starting at 140+ US med schools. (60%+ failed to start). Med schools have to start somewhere thinning out the crowd as they are simply not staffed to read/weigh out every other aspect (eg ECs) of each med school application. GPAs/MCATs provide an arguably objective way to conclude that an applicant can handle med school academics. It’s not perfect as many others probably could handle the academics and would otherwise be great MDs but get rejected because there are simply not enough seats available.
As to college itself med schools only require a college degree and completion of a school’s premed reqs. (As I understand it should be an academic not vocational degree). Med schools don’t require one to take the hardest courses one’s school offers, pretty much any BA/BS will do from most any college gives you a chance which, in part, means to be competitive, you need a high GPA (and MCAT). After that hurdle is met adcoms can dig further into an application. I don’t think med schools punt on rigor and I’m not saying rigor is of zero importance, but I think rigor consideration comes later in process and may carry more weight in deciding if an applicant should be waitlisted/rejected, or pulled from waitlist.