There are a lot of managers who would never fire someone for what I’ll call “routine underperformance” (to distinguish from harassment, job abandonment, etc.)

There are a lot of managers who would never fire someone for what I’ll call “routine underperformance” (to distinguish from harassment, job abandonment, etc.) If a company thinks some non-trivial percentage of the employee population is likely to be underperforming to the extent they should be fired, they probably should implement a URA target (or “rank and yank” or similar). I’m with you in disliking such policies, but if you want forced turnover of those ranked low-performing, you have to make it a hard policy, because human managers dislike firing low-performing employees who seem like they’re trying.