In many cases companies don't interview all the candidates before making a decision, it's more on a rolling basis. You consider each candidate separately - you interview a candidate and then decide whether to hire him/her or not.
In plenty of cases companies reject candidates who later perform successfully at similar roles, and this is the point of the parent comment. However this is kind of a desired effect, because not hiring a right candidate has lower cost than hiring a wrong candidate:
- if you skip good candidate, because you're not sure whether they'll perform well, you just wait for more candidates to apply, it just slows down the process
- if you hire wrong candidate, the candidate joins the team, underperforms and eventually is let go, but during the time that person works for you, you don't look for the right candidate for that role, which costs you more money and time
