Well, back in the day Windows didn't have a built-in zipper. Conquests final patch was released in 2005 I think. PKZip was the leading DOS zipper (I am old), but WinZip became more popular with Windows even though PKWare had a Windows product, too. Neither was free.
At some point WinRAR came out and had 30-day free trials but would keep working after the 30 days and just nag you. For some reason, possibly that, it became very popular for a while as did the .rar format.
I think you'll find many of the files you download here are pretty old. If not, maybe someone just likes WinRAR.
Anyway, there's your history lesson for today. If you want to open RAR archives,
7zip is free and does the job.
Additional fun fact: The password protection of zip files is not standardized. There are at least two or three different variants that don't work with each other, and even in recent months I have had to install a different unzipper (PKWare SecureZip in this case) to open a password-protected zip file.
Edit: My first thought when seeing this thread title was "RAWR!"
