Why has Carlsen's Elo not changed? Just looking up Carlsen's Elo and it is still 2870.

I know his next goal is to reach 2900. Did the 3 wins in the world chess championship simply not give him any rating points, or does FIDE take a long time to update ratings?

Thanks.
It does take awhile for FIDE to update their ratings, which is monthly (see article) compared to the unofficial Live ratings site at Live Ratings. But it is interesting to note that Carlsen is due for a 2 point bump according to the Live rating site.