Your examples are Americans - people who have lived in the US all their lives, speak the language, and understand/enjoy the local culture. , they might have trouble getting visas to enter and stay in European countries, depending on what their records look like; lots of kids have possession of Marijuana charges on their records... Not to mention, most European leagues have quotas on the number of foreigners who can play, as well as the need for European work permits, which can be difficult if you are not a superior talent (ie. if there is the possibility that a Euro player can be as good a prospect. For example, the Mexican youth soccer player, Carlos Vela, his rights are owned by Arsenal (bought them when he was 17 I think), but they have yet to be able to get him a work permit to play in Britain, as he had not played for the Mexican senior national team).
On top of this, there is the money thing. The wages in the NBDL are pitiful compared to most of the Euro leagues, and there are no guarantees that any player will ever make the NBA - they could have a crippling injury tomorrow. Until the NBDL wages are compe ive, I can't see you getting kids who can get proffesional contracts in Europed...