When Tiger first tried to come back on the scene after the scandal, he was very clearly head case. He was playing "golf swing" instead of golf. That is the only way to explain his horrendous short game, flubbed chips, and cold-topping fairway woods. Brandel Chamblee can be a smug, annoying guy but I believe he is correct when he says that Tiger's golf swing is the cause of a lot of his injury problems. He was constantly changing his swing and doing all sorts of incorrect things mechanically, which can easy cause a back injury.
It is pure speculation on my part with PEDs, but I think that could explain how he could go from being an elite athlete in his early 30s to being completely broken down and struggling with soft tissue injuries just several years later. His career trajectory has a lot in common with baseball players we know for a fact were juicing, and it happens in that late 30s age range.
I don't know how he is doing mentally now; probably better than several years ago, but now it appears he simply isn't physically able to play professional golf at the highest level. Now that he has gotten it figured out (at least partially) mentally, he can't physically compete anymore.