If I look backward I wouldn't see a small child right behind my vehicle. The parking sensors and backup camera would, though. That's why I feel like it's weird to look backward instead of looking at the video feed from the wide-angle camera.
E.g. Mazda 3 has that - if it detects a vehicle or even a pedestrian approaching from the side while reversing, it starts beeping and showing orange chevrons on the camera screen to alert me.
Obviously, this doesn't remove the need to look around and not rely only the sensors and cameras. The tech may fail and the ultimate responsibility is with the driver.
I check blind spots I know my camera has but then use the camera to actually back up because it's got a far better view from the back of my car than I do from the front seat.
Might be a side effect of how we're taught in the UK, but we were always told we should keep glancing in our mirrors whilst driving so it seems natural to me at least.
Even with the addition of backup cameras I still look all around and check blind spots as if I didn't have a camera. No backup camera I've used shows enough information to be confident enough otherwise.
Unless ya'll have some truly high end cars I don't see how anyone can confidently back up with just a camera and not fear hitting objects/children etc.
I never even thought about my habit until a friend who is very terrified of riding in cars told me they were made comfortable by how much I look around me while driving. Which just convinces me further that most people shouldn't be on the road.