Well, it's less that it's unpopular (People still play it) and more that non-pokefans who began playing because everyone was just stopped because the game's a one trick pony. You walk, you throw balls, you get Pokemon. people like their games to be more sophisticated these days. read more
Pokémon Go being so addicting and Pokémon Go being so unpopular are just two points in the same gamer life-cycle. When you first get the game, you want to play it so much because the elements in it have been carefully constructed to make humans engaged. One of those elements is a random reward system. You are randomly given items to play with. read more