They did release Safari for Windows. Nobody used it, and I guess they figured the cost of upkeep wasn't worth it.
It was very painful to read.
As iPhones and iPads became ubiquitous (as well as the popularity of Macs with developers) that didn't seem to be enough reason to keep it going.
I don't think Apple ever intended to win the browser war, I assume it was a means to an end. Maybe I'm wrong and someone was somewhat delusional. As a Mac lover who had a strong PC at the time it was quite pokey to try to use.
Also note that Google Chrome wasn't released until September 2008, so there was a year+ where Safari was the most prominent WebKit-based browser on Windows.