1. Because signatures break the layout of the page. Because they use up precious bandwidth, both on the server and for the modem users. And because I said so.
2. If you have some insane need to add a tiny text as signature, then by all means. No images (see above). And quite frankly, there is hardly anything you'd need to write in a signature that users can't see by
clicking on your user profile. Your posts are meant to be posts, not autobiographies.
3. With HTML you can easily break the board. Every time I've tried having a board with HTML enabled, trolls have done their best to annoy everyone using HTML's full capabilities. Practically every serious content-enhancement you can do with HTML, you can also do in BBCode.
4. Why don't people post more serious stuff on the board? Why do General and Spam account for more than half of the posts? Some people can't resist playing with smilies, and it doesn't exactly help bring the conversation to a serious level. Personally I think there are too many (and the wrong) smilies on the board, so I'm certainly not going to promote playing on the board by adding more. If you really want more, use custom ones. Unless you're too lazy, in which case I certainly don't feel it's necessary to accomodate your requests.
(Just got out of bed, feeling extraordinarily
)