Re: Why now?
In short: You are wrong!
A properly disabled military weapon CAN be owned by privat persons in germany. There are some special rules for "active military weapons" i.e I could not own a de-militarized G36, but those do not apply to the tank or AA gun. A good example is the "Technikmuseum Sinsheim" that also owns a Panther AND is a privat museum.
The steps necessary to disable a weapon are massiv and have been getting worse over the years, i.e for a rifle multiple caliber sized holes must be in the barrel. So the objects in question may no longer fulfill that rules. But THOSE rules we have due to "political correctness" and "anti gun craze" because the older variants (bolt welded IN the barrel) worked just as well.
Now I am off, polishing my pistols and rifles.