I don't think the US is lagging behind in the technology at all. Most blockchain tech is open sourced. Isn't XRP and XLM American? What about BAT or USDT. Many of of earliest adapters are from USA and silicone valley has the best programmers. On Steem many of the skilled developers are European or American.

America has the most robust financial system on the planet and isn't as quick to adopt cryptocurrency because it works. You may know many of their large corps already use some aspects of blockchain tech including banks and Visa. Tax models have to be developed along with rules.

Look at the whats going on here and the lack of ethics, it's difficult to police this stuff and ordinary Americans can easily get scammed. New coins pop up daily.

The biggest reason it's not popular is because it's difficult to make money with such a volatile asset. Americans are used to stability and high incomes. Speculating on an unregulated asset is risky when you can just go to the bank and get a much safer return which is regulated. Also I got 5 LEO from writing a post that took an hour, that's less 1/1000th of what I will earn today at work.