A reader who hits their mobile data cap after thirty minutes on your site will not be viewing any more of your ads for the next month. But if businesses were capable of thinking more than exactly one step ahead for any action they take, the tech industry wouldn't be such a shithole in the first place, of course.
I imagine people remember what site they were on when the data usage warnings came up, and they don't come back.
The question I guess is really if PC Gamer earns more by sending 100 mb / minute and chasing some eyeballs away faster, than by using a reasonable amount of data and losing eyeballs at the normal rate of attrition for written word outlets.