honestly surprised its not standard in modern shooters. squad is understandable as its a vr game and needs very high optimization to be playable in vr. anything else though really doesnt have much of an excuse
I did a bit of research.
Squad is not a VR game, its a normal fps, and dual render scope was implemented, but the performance was terrible, so it was taken out of the game, hence why its non-existent in today's Squad
From what I gathered and understood, the reason why is dual render scope so performance intensive is due to the PIP (picture in picture) system, basically displaying 2 cameras in the game. The performance goes on par with the engine, I assume Insurgency has no problem due to its old engine, and small maps to render. Squad on the other hand, as example, has maps as big a 4km, so in a way, you'd be displaying the map twice.