It's far easier to claim that the load inadvertently released due to some aircraft issue than to admit that you pressed the cargo release hook when you intended to make a radio call instead. Make an entry in the logbook, the engineers then have to take a good look, they usually find something that's chafing or corroded or something to pin the blame on and bam, there's your silver bullet. Meanwhile, that pilot learns a great lesson and either flies with the cargo hook breaker pulled, or simply doesn't make radio calls while carrying a load. Occams razor should be employed in more of these accident reports.