I'll tell you why. You are viewing popular as "being used by 20 websites" the PNG are viewing popular as "being supported by international organizations" The W3C endorses PNG and encourages people NOT to use GIF. The NIST (I believe it's the NIST) has adopted PNG as the official image standard, the US DoD (Department of Defense) has adopted PNG as an official standard, etc. You'll quickly find that most organizations that adopt standards for image formats have adopted PNG, rather than GIF. Again, you're viewing popularity as 20 sites, they view popularity as organizations that represent the opinions of millions.
And every image program recognizes and can manipulate gif? Really? Well GIMP, which is pretty much THE image editing program for Linux... it can't manipulate gif files. You assume just because the programs for Windows can manipulate a GIF that means all can. Also, many 3D rendering software programs can not save as a GIF (because GIF doesn't support enough colors), I could name maybe a dozen 3d programs that won't save as a gif. Just because the people want something doesn't mean they get it. I WANT a million dollars, I WANT a new car, I WANT a new house, I WANT a new job... well guess what? Just because I want that stuff doesn't mean I have it.
