> 3-5 years

That's maybe in Europe. Plenty of US developers those days have a litany of ~1-2 year stints at FAANGs and startups du jour in their CV.

Speaking as someone in the US, I've worked at multiple companies (some startups, some small businesses, some larger) that have either outright imploded or had mass department-level layoffs inside that 1-2 year timeframe. Some of them I would have stayed at longer than 1-2 years if I had the choice. I'm not claiming it's universal by any means, but there is a lot of volatility at US businesses in my personal experience.

And as usual, the employees get blamed. Maybe people wouldn't jump ship if companies didn't lay people off with reckless abandon, or hire sociopathic bosses to manage people, or screw them out of raises, or overwork them, or lie during the interview process.

The little people are going to do what they need to do to survive. If these multi-billion or even multi-trillion dollar companies feel some type of way about it, well, they're the ones with all the power, not us. They're more than welcome to change the culture at any time.

Companies at that level (fang,trillions) are like "alien" intelligences, like a form of slow moving AI - no human being has the ability to influence or change them in any significant manner.

True although perhaps that is part of (a), things move too fast.

Jump ship every 3-5 years because if you don’t, your wages will stagnate. A prophet has honor except in his own home as it were.