Hind sight... Think of how much money all of those SKSs would be worth on the U.S. market.
I think I can safely safe that if I had been in the NVA or the VOPO or in any sort of position of moderate power in East Germany in late 1989, with the end clearly in sight by November, I would have taken several truck loads worth of stuff, or several warehouses [if I could manage it] and stored it away in anticipation of being able to sell it in short order.
When you're in such a country and it is collapsing before your eyes, it is an open intivation to take any and all government property, especially weapons, because most of it will be destroyed by disarmament do-gooders or outraged mobs. Look at all of the books and decorations destroyed in Romania and East Germany by mobs. In East German mobs stormed the Stasi HQ and ransacked the place, mostly destroying. In Romania they destroyed most of Ceaușescu personal office possessions, his library, etc, when they stormed the central committee building. There's no reason to let his personal books and office decorations fall victim to the rage of the mob, such things should be taken and sold to collectors or preserved for a museum.
I find it somewhat odd that there aren't large numbers of the DDR-Karabiner-S floating around available for sale. Those NVA personnel had to know their careers were coming to an end, the Stasi definitely had to know that, and the Border Troops certainly knew it. You would have thought that some of them would have worked out a retirement plan involving taking hundreds of rifles from a warehouse and moving them away until they could arrange the sale.
Towards the end, when they disarmed the Kampfgruppen, there were so many weapons that had to be stored that they ran out of room and had to store many outside, and with so many personnel having deserted they had officers doing guard duty simply standing around watching over thousands of rifles stored outside.