Technically you can’t “steal” by freezing a card anyway, prepaid or not. If the card is offline-capable the transaction will go through once presented even if the card was frozen.
They can of course not get paid if the transaction is later disputed for fraud reasons, but this is a risk with all cards and has nothing to do with freezing.
A lot of airlines are using authorisation deferral though, not processing them as an offline transaction.
Essentially where they store up all the card information and then send each card for authorisation. This is different from an offline transaction (where the chip generates an authorisation code) as the issuer can’t decline these transactions.
I’ve used my card on easyJet flights plenty of times in the past with no issues however on a recent flight back from Iceland my card crashed their machine twice. I tried with a MasterCard credit card too which for some reason declined despite having plenty of available balance but didn’t crash the machine. The third card I tried, a Visa Debit worked fine.
Staff member blamed their ancient terminals, we even joked that even Ryanair have the ability to accept contactless.