Originally posted by Shawn DeSarkar: Because they dont want you to have a life and mind of your own.
At a previous place where we were involved in reviewing people's resumes, we were very curious as to gaps in employment, and changes. Gaps and changes weren't necessarily a bad thing when compared with overall market conditions at the time - it's pretty hard to find somone who worked through 2000-2003 without at least a month or two. That's a fact of life in this industry.
In fact, in a lot of cases I would cock an eyebrow at someone who went through the boom from 1996-2001 and didn't switch jobs, especially if they were young. I'd want to see a little bit of ambition and desire for change and exploration, but if the individual decribed a lot of this happenning under the same corporate umbrella that was fine too.
There aren't a lot of questions you can legitimate ask a candidate, and even fewer that you can get a totally honest answer from. Changes and gaps in employment are interesting questions, and provide interesting answers.
Your overly simplistic assertion is ridiculous. If someone was looking for work for a long time in a known good market, then that is a huge red flag for me. If times were lousy or they decided to take a few months off to travel and see the world, then that's perfectly OK or maybe even a good thing.
I've hired dozens of people (and had to fire a few). When you seea gap you wonder why. As Luke noted, we all know the history. If I see someone who got let go in NYC in Dec 2001 and wa unemployed all of 2002, I can understand why. If I see a guy unemployed for all of 2004-2005 I wonder why he couldn't find a job. But I often given candidate the benefit of the doubt until I talk to them. Hiring managers do understand layoffs, as well as raising families, personal and family illnesses and other problems, etc. I personally encourage everyone to take 6-12 months off before they're 30 to do those things that you simply don't have tim for when working (and definately won't once you have kids): travel, write, learn to sail, learn a new language, visit friends, spend time with aging relatives, etc. An employment gap is a yellow flag, whether it becomes a red one, or green one depends on your answer.