Hmm, what does jQuery provide that is so essential that someone decides to add a dependency this big for something so simple? It seems that everything requires jQuery these days, even when a 5-line for loop would do.
Ii your website uses the Google CDN to download jQuery new visitors will often not even download jQuery when arriving at your website because their browser probably has it already cached from visiting one of the dozens of other websites they have visited.
Ideally this would be solved in a similar way as when you statically link to libraries in C - the parts of your dependency are pulled in and users don't have to worry about it. (There are other issues with this of course, but they are well understood by now that someone could develop a system to mitigate that by now)
The code is pretty much idiomatic jQuery js following most of their style rules, layout rules and standard constructs so it's obviously been written as a jQuery extension. He must know jQuery well, hence why not use it?
As for why, well I spotted a bit of sizzle, jQuery.data and the event framework in one pass of a small code base. Given the nature of the library I can even guess what they're all for without reading the code.
Quite a lot more than the inevitable each that is also in there.