It's normal for Steam to see a bit of a decline in its users over the summer, but this summer has seen a surprising drop-off. Both the number of players running Steam on machines and share of those actively playing games on Steam has been on a uniquely steep decline since January 2018.
Steam Spy noted the dip on its Twitter account, taking data from SteamDB. The graph shows that though Steam saw its highest active user count over the recorded three-year period peak at 18.5 million in January of this year, the drop-off since has been substantial. In the last seven days, peak active user count was around 15 million.
The Steam Spy tweet additionally noted a drop in the share of active users playing a game at a given time over the same period, from 38% of active users to 31%.
The January surge and subsequent drop may be attributable in part to PUBG's full launch in December of last year boosting the numbers higher than normal. PUBG's player count drop since January accounts for around 2 million, nearing half of the total player loss across Steam. Whether those players are simply going on vacation or heading to Fortnite (which has its own launcher) is unknown.