And who could fault him for that. After all, why would he care or even want to invest time to make it run on Windows? It’s GPL, anyone can port it if they want to.
Git for Windows and Cygwin Git have some issues (I use them daily at work), but many of these can be entirely attributed to the limitations of Windows: CRLF, case-insensitivity in filesystems, problems with long pathnames, slow process forking, etc.
Mercurial was built for exactly the same reason (VCS for Linux), at the same time. Yet it has always been cross-platform.
Linus wrote it for Linux because he didn't care about whether it would work in Windows. No other reason.