Why do HR / recruiters care so much about gaps in employment?

I did not understand that a gap could be meaningful until they day I was face to face with an employee who had just torn the flesh off his knuckles by punching a brick wall in a fit if rage. He had been coming in late for several days and I was explaining to him he was going to need to focus on coming in on time. It seemed like a very low key chat, held outside so it was private. His response was to fly into an uncontrolled rage, chest heaving, red faced, where he body punched the wall next to us. I was shocked and asked him what was wrong. He explained that he had a problem with negative feedback, but he was getting better. The evidence was he had hit the wall rather than me. As he calmed down he explained that the break in his work record was some years in a mental institution due to assault. I was out if my depth. He was a nice guy but clearly needed more support than I was equipped for. I talked to my boss and the company got in touch with his doctor. I think everyone decided he was not ready for the workplace yet. Other gaps I have seen have been terms in prison, long illnesses, and periods of personal instability. None of those should be a bar from employment but they all indicate a need for appropriate support if an employee is going to be successful.

If a company has an HR department or is a recruitment firm, they are trying to do one difficult thing: filter resumes down to a small enough number to interview.

This is hard for them because they have no idea what they're doing. The people reviewing the resumes don't have domain expertise and are often among the least-skilled people in an org.

To make this type of activity scale, they essentially have to come up with universal filters that remove human judgment from the process. This includes removing people with gaps in their resumes.

Why doesn't this change? Because normally you have enough candidates that you can remove all the people with gaps and still have too many candidates.

When there's a labor shortage, as there is now, that doesn't apply. But a lot of recruiting operations haven't adjusted for the labor pool and are just ending up with too few candidates.

Because they have no understanding of what this work is actually like.

And hence, of the fact that sometimes you need to step back for a while just to maintain your bloody health and sanity.

I always assumed it was attempting to suss out if you'd been fired, since that naturally leads to a gap in your resume (and depending on how in demand your skills are, could lead to longer gaps).

It's also possibly just normal curiosity - most people don't have gaps in their resume.

Because they are sheep and believe a gap actually means something.