Seems like winzip and pkzip had overlapping time frames for the same function, so it basically just came down to if people were more into windows or DOS. I was using mainly DOS for stuff like that through the mid 90s (distinctly remember getting Doom 2 from a friend on about a dozen floppies that I used pk(un)zip to install), even if I was using windows alongside it. In fact I remember being vaguely annoyed when I got a computer that had windows that ran DOS, rather than the other way around (maybe it was XP?).