I can honestly say that I have given an undue amount of thought to the geopolitics of a secret biowar stockpile and have yet to come up with a satisfactory justification. Which doesn't mean there isn't one - it may say RAND corporation on my chair but I found it in an alley, after all.

My working theory of the moment is that biopreparat was allowed to thrive because it was cheap, it represented diversification, and if the Soviets could hide it so easily surely the Americans must be, too. After all, before the Soviets could do any genetic research at all they had to shake off Lysenkoism and to make any progress they had to buy French and German lab equipment. It wouldn't surprise me if it ended up being easier letting things run their course than busting it up and dealing with it. Apparently the Iraqis were literally dumping vats of anthrax to hide evidence; supposedly Gorbachev knew about biopreparat but Shevardnadze didn't.

Perimeter is easier to explain. The Soviets were never anywhere near as accomplished at nuclear war as the Americans were. We could get off a retaliatory strike in 30 minutes. The Soviets, by best estimates, were between 12 and 36 hours. They never had any first-strike doctrine because they had no illusions as to their survivability but they thought we were crazy enough to try it. Perimeter was a shortcut for a country that couldn't afford the Strategic Air Command.