Have you seen the content of spam that your blog receives or of any forum – I am pointing to the content of the spam? What do I feel is the spammers how they are made not they are planned but they are the frustrated marketers.
In blogs if you have watched closely while deleting the spam – you might have seen the language they are writing anything or just the same thing.
If the blog post is related to marketing they will be talking of medicines (that different kind of medicine 😉 ) so does any normal person would do that – I could only expect this from a frustrated user.
Then, after being spammed for once and not getting the post approved. They come again and again and post the same shit. They are really frustrated.
Moreover, they do need to get some knowledge before getting in to this spam field that there are spam guards activated in the website these days and for blogs (wordpress) a very powerful Akismet is there which can protect.
So, if spammers get some knowledge about this they would not spam or rather will think about other ways of spamming.