wall of text. Fair warning.
Im not gonna lie. When I was young, it was the fact that there was so much gore and nudity in it.
Then I got older and realized that the japanese were telling these really compelling stories that dealt with real life or mature themes over these long arcs that made you think about more than buying toys.
Meanwhile we were being force fed with cartoons that only served to make you want toys. So much that the FCC complained and they started giving these "Words of Wisdom" or whatever at the end of cartoons so it wasn't mindless violence used to shill toys to the youth.
American cartoons were basically soap operas for kids. Instead of selling cleaning products, makeup and healthcare shyt, it made us want toys.
Not to mention I grew up on Comics and Doctor Who, so the whole "Multiple Episodes for a Story" shyt wasn't new to me.
Anime was a far cry from Heroes meet same old villain and henchmen, heroes beat villain, everybody laughs at the camera, show over.
"Grown" american audiences really didn't latch on to that type of televised serial storytelling til Buffy came out. Look around today. It's an INCREDIBLY effective style of storytelling.
So after DBZ and Sailor Moon came with it, then Toonami and DBZ+Gundam Wing? A whole lot of us were hooked on it.
Despite it being cartoons.