The basic problem is it's now down to the game devs. DX11 multigpu was mostly done in drivers, so it was down to the gpu driver writers (i.e. AMD/Nvidia). The low levelness of DX12/Vulcan moves most of that work over to the game devs. For a lot of game devs it's too hard and just not worth the effort. Hence no Sli/Xfire. In one sense they are lazy. Alternatively you could argue that the shift to low level api's has made the driver writers lazy - now their job is really simple as they've pushed a lot of the work they used to do over to the game devs. Imo that's part of the reason AMD pushed low level api's so hard. DX11 and other high level api's mean gpu drivers are complex and because Nvidia had more people they would do a better job. Mantle and now Vulcan/DX12 pushes that job over to the game devs and makes driver writing simple so it effectively evens the driver writing field which suits AMD.