The problem was that while the official company line was "It's all canon folks!"

George never believed that. So throughout the Clone Wars whenever he'd come up with something that didn't fit with the EU they'd have to scramble to quickly come up with a retcon to try and make it work.

And now when he finally sat down and wrote the outlines for VII-IX, he completely ignored the EU. So characters like the Solo twins and Luke's kid are gone. There might be one or more offspring in them but they're not the same characters from the EU and more than likely won't have the same names.

And something of that magnitude simply can't be retconned away.