Even though Pokemon Go is free to play, there are microtransactions to purchase and the game has already earned over $200 million in one month.
To put this into perspective, Pokemon Go has earned more money in one month than Clash Royale and Candy Crush Saga. The former has earned $125 million in 30 days while the latter has only made $25 million in its first month.
Lifetime earnings for mobile games are really high so the Pokemon game could get up to $1 billion eventually. If Niantic is able to make the game more entertaining via new updates, players will continue to play it.