The fork happenned to a large extent for a want of control on the code base. So, it's mostly technical. WebKit has atleast 8 ports in trunk. Every part of it - networking, os, javascript engine, bindings, plugins, graphics has been hacked to death. And it has abstractions galore.
Now imagine you worked for WebKit. If you wanted to commit something, you had to test it against 8 ports. Many of these ports are cross platform. So, you are really talking about like gazillion combinations (mac, windows, linux, retina vs non-retina, os versions). It was not a happy place to develop and everyone in the project recognized this.
The pace of development was getting very slow because of the above. Apple faced this and said WebKit2 is all theirs and nobody else should really use it. Google faced this and decided to fork.
In short, most webkit devs are happy about this. It's worked out well for everyone.