Good point. Some elect to be a lifer. Reasons may be quality of life, domiciles, position, age, etc.

Let's take the age, for example. Someone age 60 may very well stay for quality of life. Weekends off, prime vacation times, best everything. Going to a major as a FO they will retire as a FO with only moderately good schedules.

On the other hand, say someone who flows to AA at age 30 - 35 years will get on an escalator.

In 10 years, more than half of those above them will retire. (Sliceback has done excellent analysis of this in the major AA subforum and a thread of AA vs SW outside of the subforum.) In less than 10 years they will be a CA or a senior FO with weekend off, etc. In a few years more than a decade, they can hold a CA on a Group 4 pay aircraft (767/777/etc).

Big hirings are going to go on for quite a few years. Even some of the recently hired FO are 50+, so will continue the bow wave even further.

The choice for someone at 30-35 would be to stay as a regional senior CA for qol or take a hit for a few years, make double+ as a CA on a major, and spend 20 years of their career with a great qol on a narrow body as a senior CA or flying a G4 aircraft across the small or large pond as a CA, with associated great qol.

It all depends on a person's personal situation. A lot of factors come into play. Everyone has to make their own decision. And, as is always said, you will know for sure if you made the right decision the day after you retire.