You do realize that the "non religious" does not mean atheist, but also includes agnostics?
Also if you look at the map you can see that the non religiousness is primarily caused by the socialist government in former east Germany not being too kind of any religion. You can even see the divide in East and West-Berlin. At the same time there is many people that are registered as protestants or catholics even though they don't feel religious. This map does not help to see such a development.
Agnostics generally don't want to force their beliefs on others though. They won't go against established science to oppose abortion, they won't advocate for laws against blasphemy, they won't usually oppose the rights of non traditional families. So agnostic is already a big win in my book.
Most moderate christians in Germany dont do any of these either.
Heck we had a catholic priest sue against the fascist party AfD for some of their posters being hate speech against trans people and drag artists. Article in German:
If we're going into details, then most agnostics are part of the atheist-umbrella.
Gnosticism refers to knowledge, Theism refers to belief.
Someone who says "it's unknowable if god exists" and doesn't actively belief (or withholds judgement) in a god is an agnostic atheist. Someone who says it's unknowable but beliefs anyway is an agnostic theist.
Most people who identify as agnostics are agnostic atheists, they do not actively belief in a god.
If you want to separate agnostics and atheists, then you reduce atheism to a small subset of gnostic atheism (it can be known if god exists and doesn't belief that god exists)