Their method actually does make sense, you just have to remember they aren't cops to solve (boring) crimes like petty theft. Why get it done as efficiently as possible when you can milk it for hours of overtime? 12 hours of footage means 6+ hours of overtime even watching it at x2 speed, and it's the kind of thing you can basically have going on in the background. Cops being willfully ignorant for their own benefit makes sense to me