Windows 7 is seven years old. It's just a reality that commercial software that old doesn't get support, unless you're an enterprise customer willing to pay for the privilege.
It did. That was the whole point of AMD64, as opposed to Itanium: It runs all the legacy crap you could possibly wish to.
For comparison, PC-DOS 2.1 wouldn't be expected to boot on a Pentium either. It's not a reasonable expectation even in compatibility-obsessed traditional Wintel land.
And DOS is even simpler to "support" because it doesn't need much.
Which is why nobody uses MacOS in production for anything but end user devices.
> old Linux kernels neither
They do. All major enterprise distributions backport drivers exactly for that reason – and unlike with Windows, you can update the kernel in place without having to touch any other part of your software stack. Your software won't care whether it's running on top of Linux 2.4 or 4.2, but it will care whether it's running on Windows 7 or Windows 10.