It's absurd that this is the case; it's purely about short-term profit, as others have said. I regularly refurbish and resell machines from more than ten years ago which run Windows 10 (or Windows 11, if you're willing to modify it to accept an installation) just fine.

For normal office or school use, there's nothing wrong with them! You need an SSD, about 8GB of RAM, and a first-generation i5 or i7 or newer, and you have a PC that is more than good enough for most people's needs.

I am worried about how my business is going to be impacted by the forced retirement of Windows 10, but, I'll adapt, just as the industry always does. Probably, that looks like installing Windows 11 on unsupported hardware with a disclaimer and instructions on how to keep it updated. It's unfortunate, but given that the alternative is enormous amounts of e-waste, I'll take it.

(For those who would say the alternative is Linux: Yes, for you or me, but not for the average customer. Linux machines won't sell.)