Here is a recent comment caught in my blog's anti-spam system: There are a lot similar. Does anybody know why someone would spam for a bunch of non-existent sites?
They are using bots which cost zero to them in terms of time and money, they may be blasting millions of these and some urls may be in error, I doubt they care much as long as some of the spams that are valid reaches you. The rest may inconvenienced everyone but this will be the least of their concerns.
It all depends on where/how the sites are hosted. While some links go for a while without getting shut down, others get complaints and get shut down within minutes.
There are some "pinheads" who think that if they spam every site they come across, at least some spam will be successful in achieving the result they intend. However, they don't realize the time they spend on doing so. Instead of spending the time learning how to increase web traffic, they take the easy course and start spamming everywhere. Also the bot thing that wisdomtool mentined.