That isn't illegal

it's up to the driver's discretion on whether they need a signature or not, even if it doesn't say a signature is required, if there's a giant ass package that they feel would be dangerous to leave out in the open, they can do that. Usually on the slip there's a part where you can sign and leave it on your door giving them permission to leave it, so...
And if it's in sorting they can't just go find it either, that's like finding a needle in a haystack.