With home Internet I have no need for unlimited data. I bumped us to 18gb and we used less than 5 and that was with streaming Sirius all I wanted.
For most people, that's just it. Unless you plan to unplug and ditch home internet, unlimited data just isn't that big of a deal for most and 4-6GB plans are more than sufficient. I like my unlimited, and I use it...but only because I can. I could easily adjust without it.
And in VZW case, like Apple they target more premium customers - not going to slaughter their profit margin to pick up volume and, in the process, commoditize the entire mobile industry.
And for people who stick with VZW for when they NEED good service - they could consider a single line on VZW and then put multiple devices on TMo or Sprint. Of course, to pay for two plans then it doesn't really save money cutting the cord.