It's partly a selfish, rational decision. In the borked world of corporate politics, firing someone on your team can reflect badly on you, or reduce your person

It's partly a selfish, rational decision. In the borked world of corporate politics, firing someone on your team can reflect badly on you, or reduce your personal power (the size of your bonus pool is often related to headcount). Do you want your boss asking: "Why did you hire them in the first place?" "Why couldn't you just train them?" etc.