Originally Posted by xliioper

Could be there is no longer bucket inventory in cheaper fare classes on flights (or there is not enough seats in cheaper buckets for the number of passengers they are trying to book at once which will force everyone into a higher fare class). It would be helpful to know dates and flights as bucket inventory availability can be looked up on EF (it's also possible to look up historical fare filings on EF if there were fare filing changes). The carriers have a lot of relatively cheap refundable fares since Covid hit when they waived changed fees and it could be every fare filing K or higher is a refundable fare.