The Ledger is designed in a way that, if tampered with, then it won't work and it becomes obsolete. Basically the Ledger itself is tamper-resistant, so there's no need for tamper-resistant seals on the packaging.
Couldn't someone just replace the entire guts with something that pretends to be a ledger though? Or manufacture a copy that looks like one and swap them?
Expenses dude. That's the equivalent of the "what if im attacked by 33 ninjas with uzis" fallacy that people who are deathly afraid of physical violence get into.