They look goddamn ridiculous. Seriously. Just because Google did it, then Apple, then others, doesn’t make it right. Squares are better for faces (because the shapes contrast) and better for iconic images as well. The circle crops iconic images needlessly.
The circle has become the default avatar frame for only 2 reasons, neither of them good. One, popularity. Everyone else is doing it, so why not WP? The other, is laziness. The only thing circular crops do to help the average photo avatar is they crop out more of the background than a square would — because there’s less space. But seriously, anyone with their head out of their ass knows enough to pick an avatar image with a plain background. This isn’t rocket science.
Come on, WordPress, go back to the squares and tell Google to take its circular BS and shove it.