United contacted me about the DOT complaint. They explained that the airline collects these taxes and fees as a "convenience" to the customer so that even though you don't fly you have your money on account with them but needs to be applied to a future reservation in exchange for this convenience.

They said it used to be that some of these fees were collected upon departure at the airport but people asked for this to be included in the ticket so this was done for convenience. There is no option to provided to pay upon actual travel.