So there are a bunch of bundles and discounts to be had which changes the pricing formula somewhat.
There's also the big time lack of competition in the US. Most have a choice of the cable company and the phone company and the phone company service is unlikely to be FTTP.
Charter aren't especially early to 3.1. Comcast have been deploying it since early 2016.
There is still no driver for Virgin Media to deploy 3.1 here. They were expecting to be at 500Mb and 10:1 downstream to upstream ratio on the top product however a lack of FTTP from Openreach at >300Mb without ridiculous price tags and deploying G.fast from PCPs rather than deeper fibre hasn't really left any need for urgency. My own, new build, area for instance doesn't even have 300Mb available yet.