Parity has gradually expanded, actually. The bluebloods became what they are due to decades of dominance. Like actual dominance, not the relative dominance that exists today with certain programs.
Well, I think some of what created that parity were actual NCAA governance decisions that limited the ability of the biggest teams to stockpile talent.
Decisions that have been undone by lawsuits and state legislatures

Scholarships dropped from unlimited, to 105 (1973, partly or wholly due to Title IX), to 95 (1978), to 85 (1992). Amateurism limitations on paying players were always there (although who knows how much they were monitored/enforced in earlier eras), and limitations on player transfers were as well.
All of that was in the service of parity. Scholarship restrictions meant that the blue bloods couldn't just stockpile talent, and transfer limits ensured that smaller teams who actually could develop players and build a program around a successful coach could at least punch above their weight class for a decade or so.
But NIL and the unlimited [immediate] transfer portal turned the entire sport into unrestricted free agency. Which now means that the bluebloods who have lots of fans [and lots of money] can simply outbid others, only having to contend with upstart teams who have deep-pocketed billionaire donors.