7zip from both a UX and feature perspective is awful compared to something like WinRAR, it is popular mainly because it provides good compression and is free, but beyond that it is eclipsed by WinRAR in almost every other front (outside of compression, the only other thing that i find 7zip good at is archive support - it supports a ton of formats including even disk images with support for various filesystems, although only for reading).
Even PeaZip has a (slightly) better UI than 7zip (and that one is also crossplatform, if you care about that stuff).
There is nothing wrong with 7zip's UI (and a program cannot be only "perfect" or "garbage", there are in-between, e.g. "mediocre" or "good enough" or other things) but WinRAR's UX is simply better.
One example, which for me is one of the most annoying aspects of using 7zip, is double clicking on an .exe file or .html file or anything in an archive that relies on other files in the archive (dlls, images, data files, whatever): 7zip extracts only the file i double clicked on, ignoring everything else whereas WinRAR extracts all files since chances are if an executable is part of an archive, it'll need the other files in the archive to work too. This means that with 7zip i have to manually unzip the archive somewhere first, usually drag and dropping the top folder in the archive (assuming it has one, many donts) in the desktop or a temp folder, then open that temp folder, run it and then delete the folder. With WinRAR i just double click the executable and WinRAR does the rest. This is very useful when i want to run some game from a gamejam, run an installer which for whatever reason isn't part of an executable, test an archived build of a project that is made up of exe+data, check an archived webpage that is made up of several html and image files, etc.
As a sidenote (and another source of frustration), 7zip also has the annoying behavior of deleting that temp file almost right after it extracts it (i'm not sure exactly how it decides that) which means that unless the associated program is fast enough to open it, it'll get deleted under its feet, creating a race condition between the associated program and 7zip.
There are other issues with 7zip as well as a lack of features (practically zero features in the self-extracting archive generator, as an example). The main reason i have it installed is because it can open more formats than WinRAR, especially useful when dealing with disk images from VirtualBox since i can simply open it with 7zip and extract files from there directly without booting the VM. But when it comes to working with zip, rar and even 7z archives, i stick with WinRAR.
BTW, the "terrible nag screens" go away from WinRAR once you buy it. It has been a while since i saw any of those.