They don't try it because they're not allowed to afaik. They don't own the rights for the Gothic series anymore.
There was an official Gothic 4 called "ArcaniA - Gothic 4" (
http://www.metacritic.com/game/pc/arcania-gothic-4) and it was horrible. Simple, stupid, bad.
Pyranha started the Risen series to get back to their roots, aka G1 & 2, but they failed it as well.
Oh, and to be honest, I liked G3. After a shitton of bugfixes of both officials and community I found it to be quite enjoyable although the endings were .. disappointing.