Microsoft sunsets their stuff all the time. It's just that they're competing with Google and Apple now, so they're actively trying to push this line to differentiate where they can.

Try to use only a ten year old printer driver sometime. It's a pain. Linux executes 20 year old code with no problem, as long as you kept all the pieces. How do they do it? Never merge anything that breaks known user space. Easy in theory, hard work in practice.

If you want to run applications from the 90s, you're likely to have more success with dosbox or wine than with a plain Windows. Didn't Microsoft completely give up on backwards emulation a few years ago and started virtualizing it instead, with mixed success?

Of course, if you really want something famous for backwards compatibility, look at OS/400 and z/OS. It's all layers of emulation from the hardware up in order to guarantee that an investment in that platform is future proof. It's all expensive in the end of course, as someone has to pay for it, but they live well on the customers who value such things. Running 50 year old code there is commonplace.