Diamagnetic levitation is extremely weak, which makes it much less practically useful, and also reduces its entertainment value (if you can levitate things 2 cm above the surface the 2 billion children in the world will be all over the stuff; the 1-2 mm you can get with bismuth diamagnetism isn't particularly impressive.
Maglev trains do not use diamagnetism or this kind of permanent magnets. They use electromagnets and sometimes much stronger rare-earth magnets, which are much more convenient and effective. Some of them do use superconductors, though, AFAIK.
