Well, Thanos accomplished what he set out to, so it's not surprising that the trailer shows him living his best life in "peace." While the titan may have fulfilled his comic destiny by snapping his massive fingers, hanging up his murder jersey, and settling down on a farm, there's still that messy business of killing his daughter plaguing him. We're pretty sure that Thanos's peaceful retirement won't be as happy as he'd imagined.
While we don't see much of the Purple One's face, we do see that his giant, meaty paw is still in the Gauntlet, and it appears pretty charred. It almost looks like the glove is burnt onto Thanos's hand, which is an appropriate physical reminder of the wreckage he's wrought.
