This is not true for most STEM faculty posts at state schools, though it may be true at medical schools. Search committees cast a wide net and focus on research quality and productivity (publications) regardless of where the research took place.
“Elitist” implies unfair discrimination, when in fact most hiring decisions and promotions are highly quantitative based on productivity in teaching, research and other metrics. Decisions are vetted through departments and several administrative committees. Everything must be documented and justified, with members of committees designated to ensure compliance with affirmative action criteria. It’s hard to imagine a more egalitarian process than selection of tenure track faculty.
The lower “tiers” are primarily teaching positions because the demand for teaching far exceeds the supply of TT faculty able to do the work. This has been the case for decades. The use of student to faculty ratios to rank campus quality has put pressure on schools to hire more instructors, often at the non tenure track tier.