I thought everyone knew the answer to this. It's fairly simple, the reason anime is so popular as amedium in japan is because it expresses everything they want but don't have;
-Dynamic hair colours / styles - lets face it Japanese hair is somewhat lacking in variation.
-Wide, beautiful, coloures eyes - japanese eyes are slitty and brown, anime eyes are anything but
-Military power - a lot of anime depicts Japan as having some kind of military power, even if unnoficial - eg FMP
-Girls that want to fuck guys (this is actually a massive problem in Japan, a staggering amount of girls don't fancy any normal japanese men at all.) See: every harem anime ever.
-Japanese Heroes- the way samurai/katana wielders/ninja appear in every godamm anime ever even though samurai were gone long ago, ninjas never existed, and how protagonists are always 'strong' in one way or another despite the average japanese male being a fat otaku)
-Other supernatural / sci fi shit; demons, mechs, or whatever.