This. For me, backing in is not about convenience or personal safety, but vehicular safety. Even with backup cameras, you're more aware of things in front of the car than behind it.
Backing out always confers a significant delay, and I would also argue that many people are exceedingly hesitant when backing out because they have almost no mental model about the physical extent of the vehicle.
I mean, the number of times I have seen people back out in a mincing, hesitant, stop-and-go fashion, yet leave nearly a full car length between their rear bumper and any obstacle behind them, is distressingly close to 100%.
Meanwhile, I can get into a totally strange vehicle and - provided I first did a walk-around to visualize it - can back up to within 15-30cm of any obstacle without tapping it. It all comes down to holding and maintaining a visual model of the vehicle in your mind, so you can better estimate how close you really are to anything behind you.