For tutorials and history on a good amount of the tech, see
http://team358.org/. A lot of teams also have some information on their websites. You'll also probably find a good amount of info just trawling through CD. We can give you more specifics if you can be more specific about what you're looking for.
As for why people join FRC, that's harder. It's whatever people can make of the program. It's really the same reason why anyone gets into a successful career. Try looking through A New Cool for stories, and just ask FRC members for their reasons.
Also, can I ask why you are looking for this information?