Because a stupid user clicks on that crap by mistake.

It is probably should already be obvious, that most of internet audience developed a habit of ignoring ads, same as TV audience did long ago, so the times of making money, like it was possible in times of debut of Google's ad-words are gone.

Almost no one clicks on an ad unless it is decorated as ordinary link, looking like a part of the site, which is plain cheating.

"Investors" who are waiting that FB will make profit on ads, well, let's say that they are naive.