7zip is popular because it's free and doesn't ask for a license like winrar used to. It's been around forever and many large corporations use it. 7zip features command-line options with 7z.exe which is great for scripting, file splitting which is good for sharing (especially large files to slow networks), multi-threading, and password encryption.
7z files also have a small header of 377abcaf271c0004, which can be easily removed/inserted for another layer of obfuscation to a file without an extension. I'm looking at you, google drive
