Hello, BrianTak.
You've probably read the Microsoft Answers announcement of end of life for Publisher as of October 2026 by now. I like your post with screen shots and explanations. Your theory about the direction of events that drove Microsoft's strategy with MS Publisher reminds me a bit of the "security by obscurity" expression. Quoting,
... I suspect that the primary reason that so few people are using Publisher is that most people who install Office 365 on Windows don't realise Publisher is included. I only know of the existence of Publisher because I used it in the pre-365 era as part of an office suite I purchased...
<snip>
... [although] Microsoft may be continuing to support it, they are hiding its existence so well that in future they'll be able to justify retiring it because "almost nobody is using it".
The causality that Diane Poremsky explained in her two answers seems more plausible: Millions of copies of MS Publisher were bundled and shipped with Office 2021 and its predecessors, but usage waned along with desktop publishing. If Publisher were highly popular, Microsoft would be happy to update and support it! There's no need to "hide" software in order to "make it so unpopular" that its retirement can be justified. Doing so would mean that Microsoft was being duplicitous to itself (employees and stockholders) not customers.
Sorry for belaboring this, but now might be my last chance to tell an MS Publisher story. It's about an acquaintance at the Federal Reserve in Washington D.C. He was there briefly during the mid-2010s, as a high level admin. (I don't work for the Fed but maybe... one day). One weekend, my fortunate friend told me his understanding of "security by obscurity". He used MS Publisher for everything for which his co-workers (and most people, at the Fed or any other organization) would use MS Word.
Why Publisher? For the following terrible reasons:
First, it helped him silo and hoard information, That's because no one else in his group knew Office included Publisher. Better yet, from his point of view, was that only he was familiar with the *.pub file format extension. So, he did his work using an application that no one else knew AND he confidently saved his files on the shared drive without worrying that anyone could access them.
He got fired after less than 6 months. He was caught using MS Word for only what he wanted to share, while lying about his *.pub file trove of information he revealed for his own advantage.