> If you trust the government to secure a massive stockpile of NBC weapons [etc]

Physical security and digital security are very different. Someone stealing a bomb is still only one bomb. Securing that bomb involves fortifying a well-defined local border. Attacking it requires personal risk that is hard to parallelize.

Digital networks can be attacked at any time from any number of opponents. These attacks are usually automated without the risk of being found by a guard with a machine gun. Stealing the escrow key database isn't merely a single bad event; it would allow access - possibly retroactively - everything supposedly protected by those key, which is presumably "everything".

> key

You seem to be using "key" to mean several different concepts.