He's had a poor season. Including challengers, he only has 5 wins this season, with 13 losses. He is looking like the type who has a career season out of the blue, and can't deal with the expectations and difference of level and opponents focus on you, and simply can't back up their results. I thought he was better than that, but maybe he's hurt or something
Otherwise, he just is another in a long line of flukish players who show everyone why they didn't make it to the top until late in their careers.