The name of the game these days for monetizing the internet is advertising. You can get paid for page views, so the trick is to sucker as many people as possible to your website. YouTube has become the #1 platform for this, but there are literally millions of pages out there that serve no function whatsoever except to display ads.
In order to attract eyeballs to your ads, you need content. So these guys grab whatever content they can find. That might be music, videos, pornography, political rants, religious rants, humor, poetry, news items, warez, video games, doesn't matter. They don't care, as long as it makes them show up in google searches.
None of it is original content. They don't care if it's useful or even accurate information. As long as they didn't have to create the content themselves, and enough viewers are tricked into loading their pages so they can collect money from their advertisers. So yes, if you offer music for download there's a chance it may also get caught in their dragnet.
But who cares? Sure, they're making money from content you own. But if you're not trying to monetize your own music anyway, then it's not money out of your pocket.