A lot of it also comes from what I think is a general misconception about what causes schools to become prominent and well known.
Historically prominent schools, whether in the United States or Europe, have been the schools that the wealthy, upper class elite attended and where their children after them attend. Of course, the upper class elite had educational options back in the 1700s whereas the children of bakers and farmers didn’t much go to school at all, so schools like Harvard and Yale weren’t the “best” schools in the 1700s they were the only real college/university type schools around.
There’s a reason so many early American leaders were graduates of either the Ivy League schools or a few of the small prestigious private schools in the South (William & Mary graduated many famous politicians of the era) it’s essentially because those were the only schools. There weren’t huge state school systems, community colleges, correspondence colleges et al.
Throughout the 19th century you saw more schools being created per capita, and the prestige of the old schools actually really started to get magnified. At one point there was prestige just in being a college or university at all, because they were so rare. During the 19th and early 20th century the old schools that used to be the “only” schools continued to attract the same people they had always attracted: the elites at the upper rungs of society. Classic old-money types, politically connected families and et cetera.
Just as the elites are drawn to institutions frequented by elites, generally those institutions will attract elite professors.
While the whole concept of “schools for the elite” certainly is part of the reason Ivy League schools continue to be so well regarded, it is also because of genuine quality at elite institutions (ivy league or not, elite certainly encompasses schools like Johns Hopkins, U. of Chicago, Stanford etc.) While their genesis as elite institutions comes from their tight association with the wealthy and the upper class, they also do genuinely have some of the best professors, best researchers, and best minds in their fields.
They also provide vastly better networking and job opportunities.
However, none of that has anything to do with how hard Math 101 or Sociology 330 is at Harvard versus the same course at the University of Tennessee. Undergraduate courses and programs in the United States are very similar. In what way do people posit Harvard makes first year calculus harder than it is at UT or Florida State? Last I checked the fundamentals of beginner’s calculus are pretty universal. Are people under the impression that elite schools have “strange grading systems” or that they make it so you have to get a 90% on all your exams to pass the class? Because that just isn’t the case.
If anything the hardest grading systems are more likely to be found in small liberal arts schools. Some of those schools have systems such as “all classes are pass fail, and a certain percentage of the class must receive a fail” or “all classes must give x % of A grades x % of B grades, x % of C grades, x % of D, and x % of fails.” I’ve known people who have said they went to schools like that, and thus I would say those systems genuinely present more difficult academics than Harvard or Yale which I know have relatively standard grading systems.
Even then, that is just talking about how difficult it is to get a good grade in a class. Even such a grading system doesn’t make Calculus I any harder to learn than it is anywhere else. So I am genuinely curious as to where people think these elite schools are making your average undergraduate program more difficult. Schools that just give away degrees wouldn’t be accredited, and there are fairly well known regional accreditation bodies in each of the regions of the country. Generally if a school meets those accreditation they are going to have roughly similar standards for curriculum.