It's understandable that English-speaking countries have lower rates, but even within English-speaking nations, the US is pretty near the bottom. (Australia is right at the bottom.)
England, America, and Australia make in interesting set of examples; each more isolated than the one before it. It's unsurprising that countries without a lot of foreign languages spoken nearby might be linguistic naifs. The US has a border with Mexico, of course; class/SES differences probably go a long way toward explaining why Mexican Spanish isn't more popular in this country.