There is a phenomenon known as "airline stink" that supposedly infects those who leave corporate to fly for the airlines (or who have previously flown for the airlines). It is pretty difficult to overcome.

There is a perception among corporate pilots that airline pilots are arrogant prima donnas who are unwilling to go the extra mile to perform the many non-flying functions that corporate pilots do every day. You won't find airline pilots vacuuming the cabin, emptying the wiffy-pot in an old Citation lav, carrying suitcases across a hot ramp. Many corporate pilots are the ones making phone calls to arrange hotels, cars, catering, hangar space, deicing. They often do their own flight planning and performance, weight and balance too. Some airline pilots (admittedly this was the case with me) are uncomfortable with the somewhat haphazard approach to standardization in most corporate flight departments. Even large departments like the one I worked for, although standardized by corporate standards, lacked the strict adherence to profiles, callouts, and checklist etiquette found in airline cockpits.

That leads many pilots to start far too many sentences with "at the airlines we did it THIS way..."

I did it too. It's frustrating to the corporate guys. But the biggest thing is that when airline types are recalled from furlough or the hiring environment improves a lot of times they quit and head back to the comfort of the 121 world. That's sticks the corporate department with the check for that $15,000+ type rating that they just paid for a few years back. After a while they think, "why hire some airline guy who is going to **** and moan the whole time about how we do things and then leave in a few years and I have to buy another new guy a type rating?"

So airline stink is a problem for folks who would like to give 121 a try and then head back to 91/135.

That was one of the things I considered carefully before I decided to return to 121. I knew that if I made that leap, ever going back to corporate again would be difficult or impossible. Corporate flying and airline flying are cousins, but the job could not be more different, and the barriers to entry reflect that.