Employees are required to book airfare through GovTrip/SATO. GovTrip only allows purchase of refundable tickets. By allowing/requiring purchase of non-refundable tickets, airfare costs would be reduced by around 50% on average (based on my own travel costs).
Under the current system, government employees would need to cancel air travel at least 50% of the time to justify refundable tickets. I can't imagine that the cancellation rate is anywhere near that.
Non-refundable tickets..... they're the only way to fly.