Why should they make it so that software that used to run on versions anterior to even XP (2 generations before actually) wouldn't anymore?
Because maintaining support for obsolete systems and methods only creates more work, and is inefficient.
64-bit Windows supports 64-bit and 32-bit software (via a kind of emulation), but not 16-bit software as this is so legacy that it got dropped. And this isn't the first instance of an older system being dropped. Windows 98 had a real DOS behind it. Then the real DOS got dropped and replaced with one within Windows running in the command prompt, so a lot of DOS games and programs stopped working with Windows ME and XP, and DOSBox emulates DOS so that we can still play them, just as you can still install virtual machines with older Windows OSes if you really want to. Can you imagine if Microsoft tried to keep support for all their OSes?
Put simply, Windows XP was released 17 years ago with the last release being 10 years ago, and it finally left support 5 years ago. 2 OS generations prior to this would be Windows 98, which was released 20 years ago, had it's latest release 19 years ago and left extended support 13 years ago. If you were writing software (like the latest Windows 10 OS), would you really want to have to consider coding practices and methods from 13 years ago, in addition to everything since then?
People learn for the new technology. If you want to support older technology too then that is additional knowledge that is required and so greater overheads on something that you won't use going forwards. And if you have to code for every possibility then you'll be coding for a very long time and bug-fixing for even longer.
Once upon a time people listened to music on tapes, but then it moved over to CDs and for a while tape decks were still present, but phased out. Now a lot of music is listened to via digital downloads. Tapes and even CDs aren't even catered for on most music players.
The same goes for storage media on computers. Tapes -> 5.25 floppy -> 3.25 floppy -> CD -> DVD -> Blu-ray -> and now there are many PCs without an optical drive at all and instead install Windows from USB or via a set up PCI-e NVMe SSD.