Jazz 1 does have a level editor, due to a large effort by a bunch of community members. Also, there is Open Jazz which is a source code remake. So, there is lot's more Jazz for Jazz 1 ;(.

Well, the thing is, our community is just too lazy to make big games with a jazz 2 feel. Like Skitch Possum, which died. As far as single player episodes go, there are plenty. Huge ones. In fact, in the works is a community built single player pack.

But the true fun of jj2 is multiplayer, not single player ;(.