Because it's unlikely he's displacing Kante at DM just yet, and Lampard is going with the pair he knows at center half (plus Silva). But a season with Wilder will be good for him, and could get him to lock in on a position (even if Wilder's center halves generally play more like midfielders). I don't think, Ryan Giggs's words aside, another year on loan would be a bad thing. Better to go somewhere you're going to play, impress, and earn it than be sitting in the reserves playing against kids.