I think for my school people did choose the right majors but the Professors were hired based on their ability to bring in research/grant money and had no interest/some even acted disgusted at having to bother to teach a class, therefore alot of the class, despite being high performers in general, found that alot of classes, almost 100% consistent with the Professors mainly focused on research as opposed to teaching, caused lower grades overall. We have a very low endowment and overall much less money than MIT, so the pressure/incentive to hire Professors based on their ability to bring money in the school always trumps their ability to teach or produce a stimulating curriculum in general.
I would say this results in higher curves due to lower test performance in classes, that do not actually result in curving everyone up to an A, and thus is perceived by the outside world as "tough grading" but I think the students are of high caliber, but really it is a result of poor teaching. If the 64 students who have made it through the first two years of a college with high grades, all go into one class, and suddenly the average is 18/100 on an exam, and the 4.0 student makes a 55/100 and also gets an F without a curve, then we could say, maybe this is an issue with the a construct of incentivizing Professors to actually bother teaching and not so much that the students werent cut out for the major.
To add more stats, according to 2013, there were 16,000 undergraduate applicants to my school with an incoming freshman class of 1,204 so similar.
But on the more general point, I don't think the main driver for the disparity between high grades in private schools is due to a scandal or grade inflation, as most of my points support, in general higher performing students get into higher performing schools and those more competitive schools are good, especially with a large applicant pool, at deciding who is capable of doing well there, though I would say MIT is much better at this than my school was.