> This is a false conclusion since less than 100% of PhDs have the ambission of professorship. It probably varies a lot by field but from anecdote most PhDs I k

> This is a false conclusion since less than 100% of PhDs have the ambission of professorship. It probably varies a lot by field but from anecdote most PhDs I know don't aim at staying longer that possibly postdoc, and even those are in minority - most are aiming for industry or research. You can't say that without factoring in that by the end of their PhDs they realize that they cannot be professors. There aren't any positions for them. Competition tends to be nasty. The career wears them down. If most PhDs had the option to stay, like say, 100 years ago, and conditions were better, the statistics would likely be very different!