I know the idea has been suggested before, but I just don't understand why it's been so disregarded.
Because Robert Jordan himself rejected it and no Japanese studio has shown an interest since.
One Japanese studio showed an interest in the early 2000s. However, they only wanted to make the first three books and then change the ending of TDR to being the Last Battle itself. RJ said no, that wouldn't cut it. That's the only interest that's ever been shown in the property from a Japanese studio.
In addition, the movie/TV rights are now held by Universal and they have been developing a live-action script, spending considerable sums (probably seven figures) in securing the rights from Red Eagle. They are not interested in an animation project which will not give them much in the way of return.
So in summary, people disregard the anime option because:
1) No anime studio is interested in doing it.
2) The one time one was, they wanted to cut the story down to nothing and Robert Jordan rejected that.
3) The TV/movie rights are now held by a studio who want to do a live-action project and are not interested at all in an animated project.
So it's currently impossible until the rights leave Universal (which might not be for years, if decades) and no-one's interested even if the rights are available.