poor support/awareness of animated PNGs has been keeping GIF well represented for ages

Neither APNG or MNG are supported in 2 of the big 3 browsers. If either format were supported in 2/3 of IE, Chrome/Webkit and Firefox/Gecko, it would get picked up by the other within 2 releases. Unfortunately the webkit/gecko guys are punting to the libpng guys, and nobody has budged.

See http://www.libpng.org/pub/mng/

Which is unsupported in every major browser.

Finally a feature browsers can compete on! :)