WinRAR in my experience has a better speed/compression ratio than 7Zip. If you need best compression 7z is probably best but it will cost you some extra time. The GUI and integration of 7Zip also aren't as polished as WinRAR's. I've been using both since their early versions and each have their individual strengths.

Subjective: WinRAR has nicer UI.

Objective: 7z (the format) doesn't have the same data recovery options as RAR. As it stands, RAR remains one of the best options for long-term archival of data for casual users thanks to its optional recovery records.

Sure, but if you are a non technical user what are you likely going to search for first.

A lot of non technical people know "winrar" and even if they don't if you search "rar file" on Google the first result is winrar.

7zip can't do all the same things. It's an incomplete WinRar clone that leaves out a lot of features and adds very little on its own, besides the 7zip format and being open source (both neat things, but that doesn't replace the long list of features it doesn't have or the worse UI)

> What I don't get is why people kept installing WinRAR

Kids those days. There are some rar archives ( with recovery record ? ) that are only readable by winrar.