Nice idea but it didn't work.
Going back through the mists of time, airlines used to provide type ratings to selected candidates on the basis of need and mutual trust. Fast forward to two decades ago, and bonds became the norm, whereby you signed a contract agreeing to repay the employers training costs (usually on a sliding scale) if you left their employment within a certain time period. The problem was, (and if you can search back far enough through these very same forums you will find ample evidence,) that many people who decided to breach the contracts felt they could do so with impunity, and whether that proved true or not, it placed the time and costs of recovery firmly in the employers court.
The advent of the Lo-Co's simply accelerated the concept that "your training costs are your responsibility." You carry the responsibility and the risk. The airline can assume you will be just as honourable and committed, but just in case you aren't, you will be picking up a significant share of the tab.
Some companies do still assume risk for the bond, but it doesn't sit well in the ryanisation concept of low cost strategy.