Of everyone I’ve managed (surely 50+ managers by now), I can only think of one who was heavily biased towards under-hiring. Most were biased towards over-hiring (some strongly so) and that’s the makeup of most companies’ middle management ranks. Many identified (often correctly) that the more people they had in their org, the more important they were. (Some leveling guidelines even make this explicit.) Add periodic freezes to the mix and this gets amplified during the “open season” times.

Every place I’ve worked I’ve heard things like “you better hire someone for that req before it goes away”, “if you think you need 4, ask for 6”, “make sure you don’t lose that backfill”, "never leave unused budget", etc.