The one airline for life thing worked great when they made money and didn't file Bankruptcy all the time.
Here is some food for thought.
What is the difference between the airline industry of 20 years ago and the airline industry of today?
20 years ago you had major airlines and you had commuter airlines. The commuter airlines were created to feed small loads of passengers to the major hubs of major carriers. Commuter airlines were never intended to be a career destination for most people and were viewed strictly as places to build time and move on.
20 years ago you didn't fly three hours on a regional jet because they were not around. What is currently served by a regional jet operated by a regional airline today was served by a mainline DC-9 or 737 (or larger in some cases) then.
Bottom line is this: the regionals were never designed to become career destinations for the average pilot. The reason many people are staying longer at a regional is not completely due to unions or management, but more so due to the current business model of the airline industry. And because of the way the regionals are set up and operated (read: low cost), it is impossible to turn those jobs into what they used to be 20 years ago with the majors.