If you were selling your car, you would get a lot of applicants if you were offering to act as a guarantor for their potential loan, but you can see the obvious pitfalls.
The inherent risks here are: that the candidate will fail to complete the course for any number of possible reasons; the airline will change their recruitment plans; the candidate will fail to meet the performance targets set down by the airline partner. Some of these risks (not all) may be insured against.
This isn't the thread for a long debate about this, but you can't compare airline training to selling a car. Airlines are offering a job, not a service. It is their responsibility to take a certain level of risk, just like every other industry.