Alternatively it could also be players who are starting to get a bit bored. After all the original Pokemon was about battling other players and trading, both of which aren’t in the game at the moment. Niantic did promise that we would get these features in the future, and that future could be fast approaching thanks to a recent data mine.
The data mine is courtesy of Redditor cokuspocus who discovered within the game’s code references made to trading, new types of incense, and also references made to legendary Pokemon. There are also hints that we could be getting more sponsored events/locations similar to what they’ve done in Japan.
Of course these references might have been in the code for a while and just not activated yet, but we suppose if anything it is an indication of what we can expect. No word on when these features will be made live, but hopefully for the sake of Pokemon GO players, it will be soon.