And a short expiration time absolutely increases security by reducing attack surface.
expired letsencrypt cert on a raspberrypi at home smells of not paying attention... with governments, there are many, many points of failure.
It's cheaper to pay someone just to take care of the certs (unless their bosses and procurement and accounting messes up) than to fix all that.
I've seen government stuff, i wouldn't touch it with a 5m pole.