The whole boom of manga and anime was because compared to TV and movies comics were cheaper and easier to get, especially in the 70’s, which is when more anime and manga were made specifically for adults and teenagers.
Since the 70’s manga and anime became a media with the same depth and sophistication as novels and film. This is true only in Japan as it stands but I think that it’ll branch out and this’ll be true in other countries as well.
After WW2 Japan was in a state of shock that they had been defeated so easily and had lost so much, so there was a gap in the heart of the Japanese people that needed to be filled, something that will spread hope and give people something to look forward to so, this was when Osama Tezuka the proclaimed god of manga, was growing up and experienced these emotions and surroundings first hand. What Tezuka did was introduce film making techniques into manga which influenced a whole new generation of comic artists. Animation came about from Tezuka’s desire to make his comics real, so it is said that all Japanese animation is basically moving comics. This is where it differs from other forms of animation where the characters are completely original, Japanese animation can be described as just moving manga.