I believe Spirit reports it's ancillary revenue. But ultimately total revenue is what's important, and you can consider the example above to be total revenue, fare+ancillary, all-inclusive in the average fare. The numbers aren't meant to be taken literally, just to show they can vary significantly.

When demand is low, as has been reported by both NK and F9, the airline can either sell less tickets at their normal fare, or sell more tickets but at a discounted rate. Either way the result is less revenue. Generally they would discount the fare to try and fill more seats, and hope that it's more opportunities at up selling ancillary revenue.

But it's clear that fare revenue is down significantly, and ancillary revenue hasn't been enough to make up the deficit.

F9 reports total revenue for the 3rd quarter 2023 as being down 3% from the same quarter in 2022. That doesn't sound like much, but that total revenue was on TWENTY PERCENT HIGHER capacity vs Q3 2022. So they flew 20% more seats than a year ago, but took in less total revenue than the same quarter a year ago! Their load factor was only down slightly, so that means the tickets are selling at a big discount.