It's about choice
I choose to pay SKY, I can watch terrestrial TV there, too, as part of that service.
I don't get a choice to not pay the BBC even though I'm possibly paying them TWICE as I pay SKY (I'd assume SKY would buy channel content from terrestrial TV, it's not 'donated').
Perhaps, though, with the proliferation of set-top style freeview boxes, TV makers might just start NOT putting 'receivers' into their sets, making them into HDMI monitors and thus making them license-free (you'd pay a license for the freeview set-top box as it's "capable of receiving"). This would be good and would create choice. They could maybe sell the freeview module separately and allow you to plug it in if you wanted it.
Doubtless Freeview wouldn't like that much as it would make them seem not very 'free' even though it's not their fault.