One thing to remember, concussions become easier to get after each one. Also the long term effects of a concussion are still relatively unknown. So it is not surprising that doctors have differing views on clearing him.
We don't know why the WWE doctor says no. We don't know why outside doctors have said yes. He has only gone to (I think) three doctors. No matter how skilled those doctors are, in the case of a concussion, it is a small sample size. Better to air on the side of caution for concussions.
WWE would be liable if anything happened to Bryan.
Also to anyone who thinks it is due to Reigns, do you really think WWE would rather fill air time with Social Outcasts than Daniel Bryan? They would love to have him back.
That's why they should release him and stop all this nonsense. If the guy wants to wrestle then let him go to another company, see if they'll hire him and let him do what he wants. If he doesn't want an on air roll other than wrestling, then why keep him. I like Daniel Bryan but I'm not one of his biggest fans. As long as he's still with the WWE and keeps getting outside doctors to say he's okay to return to the ring, you will always have conspiracy theories as to why the WWE won't let him back.
The only way to stop it is to cut him loose. Like I said, Bryan is an adult and capable of making decisions on his health. If returning to the ring is going to permanently damage him, and he decides to do it, then that's up to him. I would never want to see anything bad happen to him, and hope it doesn't, but this can't continue.