That's where the ghosting comes in. If you're always ghosting, then you always have recent people to get back to, not months old.
The pipeline isn't a lossless FIFO queue, in other words. People go in one end and are dropped out the other. In between are the recents you can call if a spot actually opens up.
Searching for people from scratch in reaction to a sudden demand will have much more latency than having someone you can pull from a recent roster of validated candidates.
It's exactly the same like how an integrated circuit can pull a sudden power demand from a capacitor placed next to it (often required by the datasheet), rather than from the power supply upstream, so there is no voltage sag affecting it and nearby components.
Or, in computing, prefetch and speculative execution, and such.
It can take months to hire a specialist from both but if you're constantly spinning plates, you have some lukewarm contacts as well as a list of obvious no's.
The pipeline isn't a lossless FIFO queue, in other words. People go in one end and are dropped out the other. In between are the recents you can call if a spot actually opens up.