You are right to be baffled. We in the US are also baffled.
The US has a horrible wireless data market. It's not like the UK or Europe in general. The companies here have a strong enough legal lobbies to keep their monopolistic control over data. We're behind in terms of the amount of bandwidth we can access and how much it costs. These companies typically make over 50% margin on profits while at the same time complain that they do not have the resources to expand bandwidth, or that the US is too geographically spread out.
Almost all the "unlimited" plans in the US actually has a limit. Typically, after a certain amount of usage, the bitrate gets capped. There are a good bit of wifi, but I suppose that then depends on if you want to find a coffee shop just to chat on FaceTime.
I'm assuming the article was written by an author living in the US.