True, but it's Good Enough for most people, who only deal with ZIP files infrequently and generally only ever encounter relatively small ones.

When I talk to these folks and probe why they think they need WinZip, they never say "oh, I was trying to uncompress a 7GB file the other day in Explorer and it took forever." They say "I'm on Windows, and this is a Zip, therefore I need WinZip." They're usually genuinely surprised to find out that this is something Windows can do all by itself.