What employers are concerned about is people problems and problem people. Dealing with problem employees is very unpleasant and a huge time sink. Since difficult people tend to have difficulty staying employed, time gaps and short engagements on resumes are a somewhat reasonable heuristic. When there are more applicants than you can interview, you have to prioritize the list somehow.
This, although it seems not everyone got the memo, hence a recent conversation I had:
https://news.ycombinator.com/item?id=31528057
> Being in any way undesirable hurts you.
Does having gaps make you so though? I'd say not necessarily. I mean, isn't there a workforce shortage at the moment?
Personally, I don't care. I just checked a recent candidate of mine and he... didn't put months in the start/end dates of his projects. If there's a gap there, I wouldn't even know.
Took probably double the amount of time to get a job. I finally asked someone why they cared? They said it looks like others were passing me up for some reason and they did not want to pick someone up who everyone else was passing up.
Hiring in many ways is a guess if you can stand to work with someone or not. Being in any way undesirable hurts you.