I use Microsoft Office on my Mac for two main reasons:
1. The first is familiarity and inertia: when I moved over from Windows to the Mac in 2012, Pages, Numbers, and Keynote weren't free at the time. I was already familiar with Office, so I bought Office 2011 for the Mac instead of buying Apple's suite which I wasn't familiar with.
As I used Office more, I slowly learned more of its features and I don't know how to do many of the things in Apple's suite that I use in Office. Even if I was willing to spend the time to learn Apple's suite, there's one feature in Word that I need for my job which Pages doesn't do: line numbers. That's a deal breaker for me. If Apple adds line numbers into Pages, I'd be willing to give it a shot.
I even spent time figuring out how to do things in Numbers that I do in Excel, to help a Mac-using friend at work who doesn't have Office. So I'll be willing to try if it does what I need.
2. The second is that I have to share files with coworkers who use Windows. You can export to Microsoft Office file formats from Apple's suite, but the conversion isn't perfect and that can be a problem. Formatting is very important in these files that I share, so I need Office to be able to work smoothly with the Windows ecosystem.
You can send PDFs to preserve formatting, but then they can't edit the files. None of us have the expensive Adobe software to edit PDFs, so that's not going to work either.
I also looked at LibreOffice, which does do line numbers in its word processing program, but the line numbers move around when the files are opened in MS Word in my experience. Sigh.