BBcode is simply for the final user
BBcode is actually difficult for the final user.
Now, if you said that final user is somewhat accustomed to it, then fine, I could agree, but that's entirely different from being "simple" (as in easy to use). Just the fact that user has to type "" is a pain in the ass. Just the fact that user has to remember to close tags with "/" is a pain in the ass. Posting URLs is difficult [url=http://omfg as well as posting images and creating lists.
Also, forget about advanced text styling via CSS, advanced text alignement, the ability to apply classes and ids to elements (all of which are available in Textile), and the fact that BBcode still outputs meaningless tags, such as <i> and <b> .
And then you miss all the advanced characters conversion, meaning that if user type "apple", with Textile quotes are converted into the actual HTML entities. Same for ellipsis, apostrophes, en dashes and em dashes, not to mention special charatcters such as à è ì ù ò and so on. And no, you don't have to learn tags for all of these, Textile does it for you in a transparent way. So, your posts are nicer and easier to read.
The selling point of BBcose is that's quite popular (for no apparent reason). But it is no better that any other parser. But if you're objective, you can even say that BBcode is actually the worst, most unuseable, difficult of the basket.