Actually it does, because with the windows git it includes it's own copy of ssh and bash, both of which will clash and fight with msys and/or other ssh installs - including the copy of ssh that microsoft themselves tuck away in \windows\system32
it's quite 'normal' for git-for-windows' ssh-agent to completely disable ssh-agent from working properly system-wide because it ends up pointing things at the wrong ssh-agent.
Pretty much all game development still happens on Windows because that's where all (or at least most of) the gamedev tools and middleware libraries are.
That's a pretty ignorant view, there's tons of developers using Windows. If you take a look at the SO survey (or similar ones), Windows has 47% in the "Professional use" category.
it's quite 'normal' for git-for-windows' ssh-agent to completely disable ssh-agent from working properly system-wide because it ends up pointing things at the wrong ssh-agent.