Package theft is a drop in the bucket for Amazon and can't amount to more than the equivalent losses from shoplifting if they ran retail stores.
There are also those genuinely concerned over $STATE$ security and working towards that as a goal.
I'm not condoning or supporting or rejecting for that matter any of the above. But it really doesn't take too much to see several reasons why this stuff happens.
As to the losses in relation to retail stores... retail stores generally have higher margins, and they still hire security staff and put up cameras.
It's also a moral outrage, when a subset of the population blatantly preys on others, and perpetrating the vast majority of thefts while constituting a tiny proportion of the population. There needs to be a strong response to these types of people for the safety of everyone else.