Seeing how similar this interface looks in all the examples makes me think this is not something the airlines did come up with themselves, but rather might be a something offered by a third party that they implement in their booking process.
I.e. not only milking the customer as much as possible by having them bid instead of fixed price upgrades, but maybe even having a third party taking a fee or commission, which will ultimately be passed on to the customer through higher prices.
This is just speculation though. Does anyone have insight into this?