When v4l2 came out, the main target were TV cards (analog TV cards, digital / satellite / cable TV was just starting for most western countries) and video capture cards. We did have webcams, but they were rare, basic, and only worked properly in movies. The top resolution was 640×480. I'd know, I had one of the best models back then, Creative Go Plus!
I've supported v4l2 across a few flamewars. In Windows back then you needed a closed source driver with a proprietary API for each TV card. It was impossible for a 3rd party application to support more than a few cards and usually you would only be able to use the software that came with the card. For Linux, if your hardware was supported, a common API was exposed. Thus any 3rd party application could take advantage of any TV card. This is why projects like MythTV were made possible and accessible to many.
Alas, I can see why a system designed over 20 years earlier, might not fit the needs for modern cameras and computational photography.
We have seen so many changes in these 20 years, that having a new library to interface with camera sensors, hardly seems something to fret over. ;)