Seriously, how is this cartoon so damned good and the comic such crap?

The three-panel format and strictures of syndication. That's why all newspaper comics are shitty, and only shitty comics end up in newspapers.

Many comics take a few years to really hit their stride, and I've always thought that the Boondocks had the potential to be really good. The first couple of years had some great moments, and it seemed to be building up to something really great, but then McGruder abandoned it to focus on the cartoon.

Therefore the cartoon is what the comic strip Boondocks could have been, while the comic strip is drawn by some webcomic fangirl (seriously) using punchlines McGruder phones in (again, literally) that he probably spends all of two seconds thinking about, as he works on the cartoon and rolls around in big piles of money (hopefully, but probably not).