Anime tends to have a pipeline. A lone auther (possibly with an illustrator) writes a light novel. Popular light novels get a manga adaptation. Really popular ones get an anime. At this point, I'm half convinced that most anime is made as an advertisement to sell more books.
This pipeline isn't exactly unique to anime. The book -> movie pipeline is very real in western media. The big difference I have noticed is actually that anime makers tend to be less visionary than western movie makers, and instead give you a much more faithful translation of the source material to the TV screen; whereas Hollywood adaptations tend to take much more creative liberty (usually for the worst).
This pipeline isn't exactly unique to anime. The book -> movie pipeline is very real in western media. The big difference I have noticed is actually that anime makers tend to be less visionary than western movie makers, and instead give you a much more faithful translation of the source material to the TV screen; whereas Hollywood adaptations tend to take much more creative liberty (usually for the worst).