@miki then they should explain this, clearly, earlier in the booking process, instead of going with this bait-and-switch strategy.
Also, explanation is not a justification. The fact we can understand why they are doing this does not make it okay for them to do this.
Finally, it's not our job to justify shitty money-grabs from huge companies. It's their problem.
One way this kind of crap stops is for us to raise the cost of such behaviour. That means naming and shaming them for it.