There are costs to onboarding a new employee (not just in money, but also in time and attention from more-tenured teammates, finding good "starter" tickets for them to work on, longer standups, interviewing their replacement after they leave, etc)

For pretty much any team, there's some ramp-up time where a new employee won't be contributing much and may be taking more time/attention from your experienced employees and manager. (explaining how the system works, code reviews, helping debug why something's not working, etc etc) There's some break-even tenure below which it's a net loss for a team to have hired someone. It'll be different for each team and also different for each new-hire. Maybe it's only a couple days, or maybe it's 6+ months. Either way, managers should at least be aware of this when making hiring decisions. (exception: unless they're at a cushy enough gig where there's not much/any pressure to deliver)