Here is the issue. Let's say Germany buys for their own forces and only for their own forces, no other goals. Fair enough, the sale won't be blocked. But, the industrial capacity for these arms is now built up in Switzerland, not in Germany, not in France.

Sometime in the future these arms you bought for your own forces are needed in a war you yourself are in. An unfortunate situation, but sometimes war is forced upon a country by others. What happens when you go to Switzerland to regenerate your arms for this unfortunate conflict you find yourself in?

Switzerland replies, "Swiss law prohibits the supply of military equipment and materials to countries involved in armed conflicts". And now, all this industrial capacity you funded for your own armed forces is unavailable to you in a war you yourself are in. You have no way to regenerate your arms. You are, as one might say, fucked.