Fuck I don't want to leave after a short stint either. But when the market is shifting fast as it has been for... my entire career, and people are getting hired in at 20%, 40% more than my salary while I'm on my third 4% CoL adjustment then yeah Imma bounce.
Workers didn't create this situation, companies did. They can figure out the consequences. Having a resume full of short stints never seems to have done me any damage and I don't buy this propaganda that it does.
I won't hire someone who has been at 5 companies in the last 3 years, for example, unless they were explicitly a contractor.
But if you're jumping every 18-24 months, that's expected in your early career. When people are talking about job hopping today, it is contextual to that.
Managers should look at a longer average stay, though there is no shame in leaving a bad situation early or staying in a great situation. (I actually don't yet know what the right timing is for a manager role, honestly, though I'd assume 24-36 months from what I've seen.)
I understand there are shitty companies. But if you're judging just by the "harshness of layoffs" you don't have the full picture.
Though to your point about laying off long term employees, depends on the country but it's often cheaper to cut shorter term ones (as they have less entitlements accrued, if that's a thing in your country). The other reason long term employees may be cut is they have accumulated too much in terms of small percentage pay bumps over the years and you end up with a team where 1 person is earning 50-100% more than the person next to them, and it's just an obvious cut.
The fact is, we are all working for a wage. With the death of unions, and right to work, that's about all we're working for, personal motivation aside.
If a company is willing to pay more to hire you than your company is willing to pay to keep you, take it. Only suckers stick around out of some loyalty. See how loyal the company is when times are tough. In my personal experience, the tenured, high paid 40 and 50 year olds are the first to get the axe.