Because it's a gif.
Gif doesn't allow for partial transparency.
(
Bob Todd whee,
Fri 10 Oct 2008, 22:54,
archived)
Oh yeah, haha
Silly me, why don't they force APNGs to have a smaller filesize?
THOSE IMAGE FORMAT BASTARDS.
(
Nathanial Hornblower,
Fri 10 Oct 2008, 22:56,
archived)