I did use Office 2003 for a very long time because of just one reason:
I hate the ribbon UI of any version of MS Office later than that one.
In 2008, I bought the 'Home and Student' version of MS Office 2007.
And then discovered that the menu structure was replaced by the ribbon structure.
But I said to myself: You should use it, certainly must get used to it.
At that time I did a lot of (private) work with Word and Excel, so the opportunity to get used to it was there.
But I failed. After about a year, struggling every time to find the functions in those silly organized 'menus', I decided to return to Office 2003 and that has stayed so until last year, when I found the Softmaker Office 2021 package, with which I could choose between Menu / Ribbon structured UI.
So I still use the menu structure of Office 2003, but in a more modern app. And I'll stay doing that until the end of my life!