Is being a job quitter common in the pilots' world?

The answer is a bit complex. To a degree, what you hear is correct - but it does not quite mean what you might otherwise think it means.

Consider your first job (maybe while in high school), working the drive-thru at McDonalds. It's a honest job, but most folks (especially youngsters) don't intend to do it for the rest of their lives. The expectations are that you will change jobs a number of times (hopefully for better jobs with better pay) before you are finally established in a career. Pilots are in a similar situation.

For many pilot jobs, especially with getting to the airlines, it is all about the hours. Those hours represent both experience (and some hours are better than other - twin engine hours are better than single, and jet is better than piston). But paying for the hours yourself is beyond the reach of most people. So pilots who want a career with the airlines usually have to start at the bottom. They scrape up enough money to get their commercial license and instructor rating, and start instructing - often in a rental plane older than they are, and for so little money that they too are working the drive-thru at McDonalds.

They accumulate enough hours (and contacts) to start helping out with late night freight delivery (called being a freight dog). Maybe get some charter work. Than a full time charter job. Move up from there to a small regional carrier or one of the charter jet companies. Then finally, if they are lucky, to the majors. And yes, this means changing jobs several times.

Now understand, some pilots love instructing and may do that for their entire time. But for most, instructing and hauling freight and the rest are just stepping stones to their "dream job."

Once with a major carrier they typically stay with that carrier if at all possible. Within the carrier, the pay and job quality and other perks are determined to a large degree by seniority. Switch to another carrier and you may lose all that hard earned seniority. [Pilots generally hate mergers and acquisitions, since that may affect their seniority, without them having any choice in the matter.]

So yes, a freshly licensed commercial pilot may indeed change jobs a number of times on the way up - but probably no worse than a lot of other career paths.