Maintaining complete compatibility with WordPress, including any future changes, while trying to clean up design problems (how is this actually possible without breaking anything?) would be a full-time unpaid job from hell and who would actually thank you for it?
Exactly. Everyone that says "fork it" also say "maintain plugin/theme compatibility". That compatibility is part of the problem. The best solution is something that is easy to install and administer for non-dev users. To get something with the extensibility of wordpress will probably take a very long time. For now we just have to deal with what wordpress is.
