Christina A. answered 04/28/20
Compositor/editor and aspiring teacher
The older anime series was created and completed before the manga was done, therefore made up its own ending and finished before resolving may of the major plot points.
The new series (started 2019) in 100% based on the manga and isn't throwing in its own filler plot lines. The goal of the new series it to animate the entire manga series (unlike the OG anime).