We're talking about law enforcement agencies, not an IT department. Of course it's technically possible to image a machine quickly. However, there are all kinds of steps and rules for chain of custody, transporting evidence, cataloging it, storing, examining it, etc. and a finite number of personnel to perform the work. Revisiting the child pornography example I used, fingerprints and DNA evidence on equipment could be quite relevant to a case. There may even be a need to examine hard drive platters (old school spinning disk, not SSD obviously) to determine if there was data deleted in the past. It's rather simplistic to say it's a matter of just imaging and returning as quickly as possible. I agree the equipment being gone often presents a hardship for a defendant, but arguing that it's intentionally set up this way to inflict cruelty ignores the reality of investigations.