sorry! Not buying it.
most people who are looking to make legitimate purchases don’t use VPNs. Who is more likely to use a VPN? A hacker.
it’s a misguided policy at best
It's certainly a blunt instrument and (relatively) easy to bypass but I have to believe the fraud prevented is worth the loss of revenue to the airline, or else they wouldn't do it as a profit-loving enterprise. In addition, I think you will find many (but certainly not all) companies have resorted to this tactic.
Using the app or website from your foreign phone (with WiFi disabled) may provide an easy workaround depending on how your mobile provider routes data.