Many schools have a bucket for first generation college students. And some private colleges limit international students to only 10% of the freshman class. Because CMU takes a greater number of full pay international students, they have less room for low income or first generation students.
Simplifying the admissions process may help a little to increase access for low income students. Harvard and MIT count “Fit” but not on campus visiting.
Pittsburgh is not as popular as Cambridge MA so “the interest factor” used to be important to CMU Admissions.