I would argue that the trend is that gaming is moving away from complex gameplay rather than away from desktop.

What we see is less complex titles released every year both on PC and console. The reason is probably because development cost is increasing super-linearly (exponentially) both as money and time. See Battlefield, CoD, Assassin's Creed, NFS... I can't imagine how much they spend on all those details (gameplay & visual)

It's easier, faster and cheaper to move towards we/mobile where the market is hot (many new people, not only fans) and the gameplay involves simple actions.