Completely by accident. There was never any intent to mine that information, no sir.
So the idea that they are playing loose with the rules on purpose based on recommendations from the top seems warranted.
The incentives are that if data is deleted, the person doing it can be in trouble for destroying it. The probability of getting in trouble for not deleting is low.
This is based off of a mentality of: If we need the data and delete it, we (the gov) will have less power. If we don't delete it and need it, we will have more.
I believe the flaw in this reasoning is not considering a 3rd possibility: We don't delete it, don't need it, but it falls into other (even less scrupulous hands) that can use it and gain power.