If it’s the same for their graduates but they make 3x, then what forces are keeping them there?
For some it’s idealism - but few tenured professors are idealists in my experience.
Second, most people aren't rational economic actors and even those who are have a myriad of objective functions.
Some common reasons people stay when they could get much higher paying and lower stress jobs:
1. Immigration.
2. Work life balance. Not unique to academia, btw. I know ex-FAANG SWEs who make $70K/yr because they can get the job done in one or two days a week from a van and want to spend most of their life in the mountains.
3. Immigration.
4. Some people actually enjoy teaching and view it as a life calling.
5. Immigration.
6. Ageism. A 50 year old who spent 20 years in academia is going to have a hard time getting back into industry.
Also, the multiple is closer to 10x for strong faculty candidates if we're talking about teaching-focused roles. A lower-tier college/university (non phd granting) will offer 60K - 80K for a full-time faculty position. A PhD with 5-10 years of industry experience will make >500K if they are maximizing for income.