but there's a lot more to it - there are schools and communities in New York, Los Angeles, Paris, ... everywhere? just as you'd find improv classes and communities all around the world.
as for motivation -- I'm not OP, but for me, it can be the same reasons that drive people to learn acting, or improv, or dancing, or meditation, or horse back riding. something about it is about exploring a new "thing" (being on stage, performing) and some is about exploring yourself (your limits, your subconscious, your inner child, etc.)
you should try it if you haven't. everyone should. :*)
Please please please elaborate on this. I can probably guess what clown school is but ... what's the motivation here?!