Barnack Or is the current way shields work a decision made to be "different" from everything else?
This - it's a decision to emphasize design and part placement. With a ship-wide bubble shield you would lose a lot of complexity (and IMO fun).
That being said, there are a lot of mods that add bubble shields. They don't work exactly like you describe, but they're still pretty cool. I've even seen one mod that adds shaped shields so you can build a custom-shape shield bubble around your ship. Not sure what any of the mods are (I don't play modded) but if you ask around I'm sure people can help you out.
