Even though the U.S. ranks pretty dismally worldwide for broadband propagation, ISPs around the country don't seem to be doing much about it. It seems that broadband growth in the U.S. is slowing down.
Despite that worldwide the U.S. is in 24th place for broadband availability, there is not enough incentive for ISPs to pick up the pace. With demand lower, due to remaining markets being "low-demand", many are not interested in getting high speed, which makes selling broadband hard.
It's not the same story coast to coast, however. Many want it, but simply do not have access. Only an estimated 31% of rural areas have broadband access, compared to 47% for urban population. With the large landmass that encompasses the U.S., some areas are difficult or near impossible to service. Other areas, however, may be just ISPs not willing to invest into something that may not make them a lot of money. Either way, the U.S. is slowing. That 24th might dip even lower.