The unspoken observation on the reason why this happens is it almost always political in the organization to make themselves more valuable and harder to fire / layoff.

That includes gate-keeping behaviour such as not handing off knowledge, sham performance reviews to prevent ambitious juniors from over-taking them (even with AI) and being over-critical to others but absent and contrarian when the same is done to them.

That leverage does not work anymore in the age of AI as having "expensive" seniors begging for a pay-rise can cost the company an extra amount of $$$. So it is temping to lay them off for another one that is a yes person that will accept less.

In the age of AI, I would now expect such experience to include both building and working at a startup instead of being difficult to work with for the sake of a performance review.