USMCFLYR,
The simplest way to explain it is that in most cases, the companies who ask new hires to sign training contracts are the ones that aren't as "good" to work for. By "good", I mean, pilot friendly workrules, commutable schedules, etc.
When a company locks in a pilot for a year with a training contract, it nullifies the effect that a bunch of pilots leaving because they hate working there would have, thus making it difficult for any improvements to occur.
TC's in effect are a way to skew the labor economics of pilots, making it more difficult for them to "vote with their feet" when pilots feel they aren't treated well or fairly.
Checko