Qt doesn’t cut it; it’s designed for something completely different: windowed GUIs, not (3D) games. It’s the same reason why you wouldn’t make a game using WinForms. Basically, games use a different architecture than GUIs.

SDL w/OpenGL more or less covers the big three though

SDL probably isn't performant enough for AAA titles.

Uninformed nonsense, SDL gives you the graphics context and you directly use native calls. It even supports Vulkan these days.

Hence the probably part of my comment. I wasn't speaking as an SDL authority.

They could have used Unity to get good Windows and mac OS support, and theoretical Linux support, but that's a decision they would have had to make from the very start.

Because they still need to the QA work for each supported platform.

Develop once, debug everywhere.