That doesn't make any sense at all. That sounds like some sort of anti-trust issue that keeps airline costs low by making it impossible to "poach" highly qualified pilots from other carriers and raise wages.
To quote a letter to the editor in 2003 WSJ https://www.wsj.com/articles/SB105149633146672400
"A 45-year-old captain who has been with an airline for 15 years cannot quit and go elsewhere, because doing so would mean starting all over at the bottom, earning $25,000 a year at a new airline and working every holiday. Imagine if a surgeon had to go back to being an intern every time he changed hospitals."
It's exploitable somewhat by airline management (definitely takes the metaphor of golden handcuffs to the next level), but then the number of airlines is not fixed, with new start-ups coming on board every few years or so, so you'd think that at least someone would exploit these inefficiencies, if it made economic sense for them.