I'm not sure, really. I've searched on it a bit and don't see a lot of good sources on explicitly why it doesn't work well, but I see the vast majority of user

I'm not sure, really. I've searched on it a bit and don't see a lot of good sources on explicitly why it doesn't work well, but I see the vast majority of user opinion is the same. This is a bit anecdotal, and I don't have expertise in the underlying technology, but I read mentions of requiring use of specific driver functionality to get better performance out of an SLI or dual GPU setup, via mechanisms like using a dedicated GPU to render each eye independently from each other instead of attempting to render both images together on a bridged virtual card. Allegedly, it's a bit of extra effort to do this (as they'd need to support both the AMD LiquidVR and Nvidia VRWorks) and would only benefit a minimal audience, so other aspects of the game get prioritized for development effort. There are a couple of implementations that do. eg, Nvidia Funhouse VR was a showcase app of what implementing their SDK could do and they used it. I think Serious Sam VR used it, but I haven't tried that game..