Their most well-known title, World of Warcraft, reached 12 million players at its peak, but ended up at less-than-half of that at the end of 2015. While Blizzard said they would no longer report WoW subscriber numbers in 2016, they are more than excited to share their player numbers for Overwatch.
To be fair, Overwatch requires no additional monthly subscription cost (unlike World of Warcraft). Also, as of now Blizzard Entertainment has said that all downloadable content will be free. The only investment required for the game is the initial $40.
I believe this was a smart decision for Blizzard— they had tangible proof from World of Warcraft’s decline that the monthly subscription model was not working anymore. Also, I believe forgoing the monthly subscription allows them to capture much more of the teenage market (who often do not have credit cards).
By building their audience as much as possible, Blizzard is slated to earn large returns in the future with the inevitable release of expansions and eventual paid DLC.