People go with what they are used to.
Ease of use. Most UNIX programs accomplish a lot, without dragging the system down, generally because they do one thing very well, without a fancy user interface. Although winsock.h was easy to find, some of the more esoteric headers had to be built from scratch. In order to do NcFTP, I had to also port Curses, but normal DOS screen IO was horribly inefficient, so curses had to be ported to use Win32 Console mode function. Fortunately, somebody had already ported Curses to dos, so I just built on that.