What's the point to these pixel ads? How can they benefit so much? They seem quite expensive for a little images.

No point to them at all
It's known as "buzz" marketing. Come up with an idea that generates a lot of short term interest (a media buzz) and capitalise on it while it lasts.

The current crop of sites are simply copycats and "me toos" who will find they are too late and their money making scheme site will just become more internet detrius.

I agree with Chris. This won't last.