So why aren't employers doing more to offboard folks with grace, kindness, and compassion (and maybe some degree of expected severance given the goal) if they are really "sacrificing their potential for the team's success" when all that's needed is for the employee to realize they need to move on?

Is loyalty to any employer so utterly and completely dead that I need to enter my future employer-employee relationships with different expectations about loyalty after 1/2/4/5 years?

I'm incredibly fortunate to have lucked out at a place that was acquired 2 weeks after I was let go for being in a similar place as you can imagine when someone spends 4 years somewhere without a promotion or any material recognition of that loyalty. So my 4 years was worth something - at least the after-tax value of my exercised and liquidated stock options.

But that's an incredibly risky basis for value gained by staying somewhere vs. value gained by going somewhere else.