Because you've not paid for flexibility, you've paid for a very specific thing that can't be changed.
It's like the all-you-can-eat restaurants which charge you extra for stuff you don't eat. If you went to a regular restaurant and they tried to charge you for food you didn't eat that would...
All right Easy i've got one. You go to the butchers and ask for a kilo of fillet steak. You then say as a favour could he mince the fillet steak for you. When you go to pay would you argue that you shouldn't pay fillet steak price per kilo you should pay beef mince price per kilo as that's what...
Well there are all-you-can-eat restaruants where you have to pay extra for any good you take but don't eat. So basically you're getting something cheap, but they might punish if you break their terms and conditions
I got fined when I was a student for trying to get out at New Cross station as I had a ticket to 'London station #' or whatever it says and the Brighton to London Bridge train goes through New Cross and stops there. I didn't think it worth informing the press about this
Most of you seem to be complaining about the existence of cheap fares, which is a little odd.
It's surely better to sell cheap tickets with restrictions than not to offer cheap tickets at all