Since when has coherency and proper grammar mattered on the internet at large? Bottom line is that it's more cost effective to take a lower sales to spam ratio due to bad grammar than it is to hire someone to proof the spam. Then again, I suspect that all that spam advertising spectacular paying internet jobs might just involve a little proof reading.
But some of them are actually kind of clever, such as the guy with the NASA moon mission post
peppered with links to boner pill stores that should
have been hidden behind images. All that spammer did was lift the text of an article and replace the images with his own spam.
If I remember my statistics, it's something like 500 click-throughs and one sale per 150,000 pieces of spam that actually make it to human eyeballs. From the spammer's point of view it takes something like 10,000,000 pieces of spam sent per sale. Spam is pretty damn cheap, though, and the profit margins of what they're selling can absorb all that spam, so it remains profitable. Couple hundred million dollars a year profitable.