1. Could be that they're willing to take the risk.
2. Could be unaware that the mic or interface is even capable of doing that.
3. Larger content creators could also have sound guys keeping an eye on things behind the scenes, thus negating the need to monitor it personally.

They listen to what's being recorded by the mic in real time, as opposed to after the fact with computer playback. It's there as a measure to help them record better audio because they'll pickup that something is wrong while recording instead of after the fact when listening back to the audio after recording an hour of unusable audio because whatever audio is being created by the mic will be heard in the headphones as they are recording.

To monitor the audio in real time. This is why zero latency monitoring is something brought up fairly often in audio interface reviews and something a lot of podcasters and whatnot tend to (rightly) care about.