As birdie already has pointed out, it's probably due to Steam entering China. China is reported to be one of the lowest linux adoption per capita country:
http://i.imgur.com/FXfa5vA.png
https://gs.statcounter.com/os-market.../desktop/china
http://i.imgur.com/FXfa5vA.png
https://gs.statcounter.com/os-market.../desktop/china
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