Can anyone explain exactly WHY Apple will cause 32 bit apps to stop functioning?

We are not Apple, just other users and therefore have no idea why Apple would decide to do something (or not). We are also not allowed to speculate, so we really have no way to answer your question.

As for your old MS apps: it is up to the developer to keep their apps compatible with new OS versions. Most support their apps for a period of time and then decide that they need/want you to buy newer versions because they need/want to keep making money. There is no developer anywhere who will support/update their products for free forever. That includes mfr's of printers, etc. as well - and computers, etc - an endless list.

32-bit has been on the way out (so to speak) for some time, so you'll need to make a decision when the next OS is introduced: do you want to stay with what you have now or update.

Out of curiosity: what is a sophist?

But I'm still curious what makes it so difficult for Apple to retain feature that some users (like me) consider valuable.

All "features" require an immense amount of support. Even if nothing is changed that would affect the feature, the feature must be thoroughly tested with every update. That is expensive.

You can actually get Microsoft to provide security updates for Windows XP if you pay them something like $500,000 annually.

Developers were told to get their feces in one sock eight OS's ago. It's time for them to move forward. If you need to use a 32-bit app that the developer has abandoned, just don't upgrade your OS.

On speculation, I was not aware that speculation is not allowed

It's right there under Section 2.1.1:

Apple Support Communities Use Agreement - Apple Community

It's a solution that would fall under Occam's razor.

There is no difficulty here. Simply don't upgrade. Your problem is solved.

If you want to know why Apple do the things they do, you'll need to ask them. They're not here.