The real question is why someone could ever pay a flat fee for an infinite resource. It was obvious that could never last.
The people that scream the loudest about it, are of course the ones abusing the system and hastening its demise...
So if it was clear that it would never last, why then did companies offer it in the first place without clearly stating that this is temporary and will go away in the near future.. We all know why..
As for abusing the system.. Again, this is BS.. My wife's AT&T unlimited data plan which was grandfathered was hobbled because she used 3 or 4 GB one month. This is hardly us abusing the system the most.. We left for T-Mobile and have been significantly happier with their offerings. Fortunately we had a choice since cellular carriers are not as bad a monopoly as high speed internet providers for homes. If there was a similar provider in areas which Comcast covers and if that provider offered similar services for less, you would see people leaving in droves. Comcast knows that no such competition exists (thanks to their bought politicians) and so they can continue to screw over people and treat them like crap with little concern of losing customers.
Hell, the reason that so many people are cutting the cord is that they want to get away from what Comcast and others force upon them with tiered pricing etc.