Yeah he has time to think when the opponent is moving, but 30 seconds just isn't a lot of time if you consider there is a minimum practical time per move just based on the physical reality of being a human that has to move the piece and hit the clock, as illustrated pretty well by Carlsen's move where he knocked over a piece and burnt something like 3 seconds on one move.

I think any decently skilled (but non-world-class) chess player could have run him down just by playing defensively. Of course, that would have been terrible tv, so we got someone who probably only plays casually getting steam-rolled by the "Justin Bieber of chess".