Several reasons for spam. First is exactly what we're talking about here: there's competition out there and no rules to keep spam out (or ways to identify where they come from for that matter. If you don't want to come around anymore because of the spam then you're more likely to click around in another site. The second reason is the links you find within. They may link you to seemingly useless shut but they've got a lot of information about you once you pass through. That data is worth real money to marketing firms. Last is that the more data they get from forum text the better they can get at fooling you that they're real. Machine learning is actually very easy to implement and if they can use it to improve the text generated or figure out what makes you click on order to pass another 20℅ of users onto their nedarious websites the better off they are.
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