Why do people "spam" my blog

Okay, I'm not sure if "spam" is the right term, but people advertise their stupid crap in the comment section of my blog. For example, look under my last entry's comment section. Does this person really think more than two people are going to look at their comment? There has to be more efficient ways to advertise, are they that desperate? I've got more news for them, none of my friends are stupid enough to buy into their crap anyways. So go away!