Stablecoins are crypto. In any case, people trade things away because they have a particular need for something else. Holding currency won't fly you to Guam, but being willing to spend some will.
However, I don't see buying flights with crypto to be a real value add for most people. Usually crypto has a privacy advantage over card payments, but in this case it doesn't because your airfare info is a lot easier to look up in a sketchy database than your credit card statements are. Maybe this is convenient for the small amount of wealthy people who live internationally and keep a lot of money outside of banks. If the business isn't expensive to run, then perhaps it'll still make decent money.