I don't think that's the sole reason. I don't know anyone who uses WordPad. Like you said, for quick text edits people use Notepad or some other simple text editor and for anything more sophisticated than that people use a full office suite like LibreOffice or MS Office or pirated copies thereof.
It just doesn't make sense to maintain a third word processor software that nobody bothers to really use.
He used it in the context that whenever either me or my brother complained to him about something, it was because both parties usually were guilty of starting shit and just one of us was complaining about it.
My father used to love saying: "It takes two to tango"
I never understood the appeal of paid programs. 7-Zip works equally well and is free and open source software. It integrates much nicer into File Explorer as well.
The existence of a way to get around the problem doesn't mean the problem is solved. If a lot of people want to do this, then it should be easier to do and obvious how to do it