I think its just poorly made, it fluctuates between 50/75% but looks flatter than it is. Its hard to not bias oneself living through early multiplay, felt like it was only dudes. Women tend gravitate to single player games especially with how hostile multi-player used to be....
Also the graph is hard to find legitimate. Back in 2006 phones did not have games to the same degree and accessibility, and the trend it shows claims to be relatively flat for the last 20 years, which is ludicrous especially if it includes all games