There's an optimal pricing for most services. Take cable TV - lower the price and a few more people will buy in. But, not enough to make up for the lost revenue from lower prices. Raise the prices and you'll get more money, but not enough to make up for the people leaving your service. Your pricing can deviate around that "sweet spot", but not by a huge amount.
That's why companies instead try to make their services shittier, by inserting ads and reducing quality and so forth. People are more willing to put up with that. But if you legislate that they can no longer provide shitty service, it doesn't necessarily mean the prices will increase accordingly. Even if ISPs start lowering their data caps, people will likely perceive that as "paying more for less".
I can't help but see this as anything but a win for the consumer.