Good question. I'm pretty open on that. The primary reason we did it was that people were taking our (free) manuals and reselling them on eBay. I felt bad for the poor people who were paying money for something that we were giving away. The non-commercial CC license lets us tell them to knock it off.
Tim is absolutely welcome to publish every single iFixit manual on his site. Heck, I'll give him an archive file if he wants.
Bottom-line: We want the manuals to get used. Whatever we can do to help people fix things, we'll get behind. That's why we do the bittorrent download of all our manuals. (Speaking of which, it's a bit out of date. I'll see if we can get updated ISOs pushed out in a few weeks.) We handle sites that run advertising pretty generously—we're happy to share if they're adding value (usually by translating the manuals).
By the way—the license only applies to distribution, not use. Hundreds of thousands of techs use iFixit manuals to sell their repair services and make a living. Many of them do pretty darn well for themselves. They are all awesome.