Why top firms fire good workers

Evil

No. The reason top firms part ways with good workers is usually political. Either the manager doesn't like the person regardless of their work abilities, or the manager is not politely savvy enough to ensure their team is being recognized for work that grows or is valuable to the business. Or they get caught up in the endlessly popular reorgs (again management failure). It's a failure of management. Nothing more. Nothing less. A healthy market would encourage good workers to move around freely (through compensation, opportunity, benefits, location, etc..), not force their hand. And healthy organizations would recognize talent and retain/retrain as needed.

I think the other thing that's perhaps missing is that some companies have so much momentum (with thousands of people) that it probably doesn't matter when they lose people. The company will continue to thrive because there is demand for the product.

How to tell that some "researchers" spent too much time in economics classes and not enough time in ethics classes: they publish stuff like this (source [0]).

[0]: https://www.aeaweb.org/articles?id=10.1257/aer.20200169

It looks (to me) like they're saying that the margin (amount that firms can charge clients less the cost of the employee's compensation package) is what's at stake.

As employees rise up the corporate ladder, their compensation packages increase, but the amount that the company can charge for that employee's work is limited (clients will be wanting to keep a certain margin for themselves too)