If my ISP can only afford to supply me with 1TB of transfer at 1Gbit, that's fine. They can put it in the adverts, the contracts, and the pricing. For customers who want 10TB of transfer, they can offer a higher cost option.

And if they choose to gamble, advertising and entering into contracts promising "unlimited data", which they think will be more profitable across their entire customer base? Then they've got to do supply what they promised in the adverts. They chose to gamble that way, and if they lose money gambling that's their business.