I totally get what you're saying and agree with it although one important thing needs to be pointed out… it's actually not funny!
My guess that this is intentional to get "us" to either upgrade to Catalina/Big Sur else but new computers. Interesting this happens to only the last version that runs 32-bit software.
I had the exact same thing happen when Apple released iOS 7. That "upgrade" made my iPhone SE (update - iPhone 4s, not SE) burn up like crazy when wifi was on. At the time, no wifi meant my iPhone was basically useless. It took Apple close to 4 months to fix it. I had actually set a date that if a fix wasn't released I was switching to an Android. The update that fixed it appears literally 3 days before that assigned date. And as a side note, my primary phone is a Samsung Galaxy S10 and I'm currently eying off the S21 Ultra.
Windows is looking pretty good to me right now. 😕
It's funny (!) that you should bring this up. I was out hiking about and gave some thought to this.
Whether intentional or not, my conclusion is that this is Apple's way of telling us that:
A) We should buy applications directly from the developers. Most apps I use are available that way. So, unless I am desperate for an app only available from the App Store, I'll only buy apps from the developer.
B) It's a bad idea to upgrade the operating system beyond what came with the hardware. ("Point" or security upgrades don't count) Apple develops new software to work with new hardware that they want to sell you. How much regression testing they do on older hardware is a mystery. Whether they have a strong interest in fixing bugs is another mystery. They make no money on upgrades, so that might be a good clue about this.
Personally, I get the sense that things weren't quite this way in years past. Certainly, there was no etched-in-stone rule that new Apple operating system major versions had to come out each year at a certain time. But, who knows?
As for Windows, I have two specific data points.
The laptop issued to me by my employer is a Lenovo W520 that's about 10 years old. I'm the second user. It started with Windows XP and then was upgraded to Windows 7. (Companies often are slow adopters of new software) A couple years ago, the change was made to Windows 10. It has an i7 processor, however much memory can be installed, and an SSD, just recently upgraded again. I've used this same computer over the years to do thousands of hours of engineering simulations. Are new computers faster? Certainly. But, it still works. And, companies are cheap.
Out of those Windows versions, 7 was by far the most reliable, stable, and easy to use. At least in my experience. Newer versions of Windows make unannounced changes that can kill applications without warning and make add-on hardware like test equipment useless. Please don't ask how I know this.
But, I do have a white iMac circa mid-2006 with a Core 2 Duo that runs Windows 7 very well.
Overall, the Mac system is much better in pretty much every way. But, they sure make it hard. Harder than it needs to be, as proven by how much easier it worked previously.