I'd invite you to ask a few poor people what happened the last time the government "definitely sent" some important document or another in the mail.

If a governmental employee gets the address wrong, gets the name wrong, accidentally knocks the mail in the trash, lazily marks the job as complete without sending anything, etc, the burden shifts to the poor person to prove not just that they didn't receive the mail but that the sending office didn't behave correctly.

Other cases behave similarly. In a he-said/she-said, the government wins.