The high mobility part is overblown.
The biggest teaching factories are also the ones who spend exorbitant amounts on bureaucracy and accessories while gratuitously taking advantage of young people eager to prove themselves, having little to no responsibilities and no understanding of the professional world. Their whole shtick is to find suckers willing to stick after, all the while taking advantage of naïve youth.
The vast majority of people don't move if you keep their pays on actual market rates. Interviewing is a chore. Moving for jobs is a chore. Most people hate getting out of their comfort zone. Yet, many will push individuals to 'prove themselves' first, having any pay raises lag behind for several years, where individuals find themselves getting their promotion's worth of money only after moving to a different company.
It's the companies that have optimized for this behavior and chosen internal promotions should be few and unrewarding. Not the other way around. God forbid they reap what they sow.