Most people with "unlimited" data will probably use anywhere between 3-10GB.
But there are people, on the same unlimited plan, that will use 100 or 200 or more GB a month. Now, since they bought "unlimited" data, this is fine. They're getting what they paid for. Some might argue that they are abusing the service, but that doesn't matter: they bought unlimited data, so they're using it.
The result is that people who might use less than 10GB of data a month by streaming lots of music and youtube video, are put into the same service tier as people who might basically run torrents on their phone, or even use it as their home broadband, racking up hundreds of GBs of data a month.
I think part of the problem is that right now the data tiers are silly. Plans basically offer triers that look like this:
There's this huge spike.
People who will stream slightly mare than average, and people who intend to use their data for massive broadband demands will have no choice but to go with the unlimited plan. How about some more reasonable tiers? Something like
I lost track of what my point was supposed to be so I'm going to stop typing now.