They don't know how to fix it. Ok.
They do. NXT is the current good version of WWEs product that is appealing to children, teenagers and adults. That style of product could work mainstream, but it would mean WWE would have to change many of the core ideals they have in place on their mainstream product.
The big issues with mainstream WWE is that they are scared for people to outright fail. They will either give people a chance and quickly pull them, or run an idea into the ground until it gains more acceptance. NXT is more reactionary and can adapt, but the main product currently lacks that. In NXT wrestlers can fail, learn from it, grow as a performer, and come back better. Failing on the main product means you are fucked.
A big change they could make on the main product is to give people a chance to fuck up and recover. People should not be afraid to fail, that means they are never going to try, and it means creative will never give them any risky material.
The more I think about it, the more I believe the main product cannot be fixed by patching wounds, it need to be rebuilt from the ground up with new ideals in place for everyone that works there - backstage and in the ring.
NXT is a great template to start from if they are willing to.