The New Yorker ran a piece explaining incentive for airlines to ensure that your flight experiences are terrible.
In their own words:
[T]he fee model comes with systematic costs that are not immediately obvious. Here’s the thing: in order for fees to work, there needs be something worth paying to avoid. That necessitates, at some level, a strategy that can be described as “calculated misery.” Basic service, without fees, must be sufficiently degraded in order to make people want to pay to escape it.