Why? Because you always have idoits wanting to destory them. I've seen a lot of spam on wikis in my time (I didn't join until this year but I still used them). Some wikis are either lucky or just have better spam bockers (or are just super fast so they changed the page back before I find out about it). I know that the Call Of Duty wiki had some spam that I remeber, somebody deleted the text on the 'A10 Warthog' page and put in its place "I LIKE TURTLES." Of course, that was changed back within the week.
I'm not saying this wiki has horrible issues with spam, because I've seen worse. I've seen wikis that bearly have an content at all. They'll have This person is a charater on this show and nothing else. Not even telling me if the person is male or female.
So until we can rid the world of spamers, we keep working of changing what the stupidly mess up.