This is very upsetting to me–more as a point of principle than in fact–but I appreciate that it doesn’t bother younger generations at all.
I am in a support group with over 100 senior citizens in it. Getting a file with a *.rtf extension used to be a thing, but it hasn’t been a thing in years. I do get *.doc and *.docx files so they’re probably getting lured into Office like you said even before Wordpad is removed.
This appeared this week on our home Windows 10 machine as well for the one account that does not use a Microsoft account. It’s a new behavior.