I went through the entire thing just to find out people wanted the girls to die...
The point of the story is there is always hope. This is not a conventional zombie story like the western walking dead series where it alludes the only way out is dying.
Sometimes we forget that the point of survival stories is to survive long enough until things go back to normal.
All I see with people disliking this ending is doomer mentality taking over and hoping for the cute schoolgirl daily life story to focus on the zombie aspect...
...And getting to a point where we forget that japan does things in a different way that we are used to.
I too have shared the frustration of endings not being the way we imagined, but the story did come full circle with its characters and is pretty well rounded in its elements. The thing I then sense being is not one beat of the story follows anything I have seen before in the genre.
The series as a whole took a different approach at what I think is a stagnant genre and I respect it for it.