Because I use winrar and I'm so used to using it. It can also compress the files better than zip last I remember. 7zip can open rar files as well. .w.
Wow I genuinely didn't know 7zip existed. *scrubs WinZip free trial out of my computer with lysol*
The last time I saw a rar file was in the days of "You are on day 7 million of your 30 day WinRAR free trial". I basically associate them with trying to sneak files past your antivirus and nothing else. I don't feel like better compression is all that important considering I'm not on dial-up, but I guess it's fine.