I think a major downfall of anyone outside of the big 3 is the fact that Airlines have turned into financial institutions. Loyalty benefits, cobranded credit cards, frequent flyer programs, etc. These programs now bring a lot of revenue and offer upfront payment to the airlines for miles sold to institutions. Far outweighing ancillary fees which
Spirit was known for.

Now if you were to sign up for a credit card would you take a hard inquiry to sign up for TrueBlue, where one will always have to go through JFK or BOS or for a legacy card with lounge access and a global network.