A large part of that is that its engineering/CS departments are at the very apex alongside MIT/Caltech/Berkeley/Stanford.
In comparison, even the Ivies with nearly comparable strong engineering departments such as Princeton, Cornell, and Columbia SEAS come up short and have stiff competition from schools like Georgia Tech, UMIch, UIUC, UW-Seattle, etc.
And the rest of the Ivies are well below them among the engineering/CS set…especially back when I was in HS/college. In fact, this was one major reason why when one HS classmate turned down MIT for Harvard intending to major in engineering, most of the aspiring engineering/CS major HS classmates wondered if she had flipped/what funky drugs was she smoking.
And she came to agree with them as when she attended Harvard DEAS in the mid-late '90s, she felt it was “the neglected stepchild of FAS” in her words. This was further reinforced when she attended Stanford for engineering grad school and felt if she had to do it again, she would have taken that MIT offer.
As for LACs, at my STEM-centered public magnet, while there was a definite bias in favor of universities, some LACs were considered on/very close to par prestige-wise as HYPS…SWAMP*. Also, despite its lowish USNWR ranking, Reed was also considered top-shelf elite.
One thing to also consider is one reason why some at my HS turned down admission offers to some of those LACs had much more to do with fear of enduring overwhelmingly great rigor/workloads than they would have had based on rep and reports from older classmates/alums who attended if they attended the Ivies…including HYP.
Like UChicago, Cornell, JHU, or MIT/Caltech/CMU(engineering/CS), some of the top LACs…especially Swat and Reed were sardonically joked by some of us as schools which were so difficult that odds are we’d graduate in a box because the overwhelming workload/rigor meant we wouldn’t be able to walk on our own power by the time graduation rolled around.
HYP and other peer elites had no such reputations backed up by dozens of testimonials from older alums who have attended. If anything, the vast majority of classmates who attended HYP found the academics…including the STEM majors to be easier/more enjoyable than those at our public magnet HS.
*Swat, Williams, Amherst, Midd, Pomona. Add Wellesley if one’s including women’s colleges.