The govt key decrypts everything, real-time and stored/archived, sent in that nation during the time it is in use, and that key is in use in multiple places/machines, and is in an org that is a high-profile target for many other reasons (so could likely be exposed in a crack that initially had other purposes.

In contrast, a person's key can decrypt only that person's messages, is used only in one place (usermset of machines), and is a generally low-value target.

Insanely huge difference between losing a person's key vs the key to an entire nation's communications, even if it is the key of the nation's president -- still far lower value & consequences (start with: if you have the nation's key you can decrypt the president's comms anyway).