Though One Pocket may not be very popular outside the USA it is gaining in many European countries and Canada. I know this to be true because of the numbers of books I have personally sold to these countries. The Netherlands, Poland, Finland, Switzerland, Germany, and of course, Canada.
There are quite a number of very fine One Pocket players in these countries. Without naming names, there are several very accomplished players who though not known as "One Pocket specialist" are still very strong at the game.
One reason you may not hear much about them is the sparse number of tournaments here in the USA and their moderate pay scale. The overhead for anyone coming from Europe to the US for a tournament just doesn't justify the trip.
That said, in my humble opinion, the game is so great and demanding of all cueing skills it will continually grow in popularity throughout the world. Give it time. The game will have its day.
Thanks,
Tom