Software engineer / developer here. I can.
You provide a lot of what-ifs, but leave out the most important one: what if Adobe developers were at least remotely competent at cross-platform development, and created an actual API that they would code to. Implement that API once across each supported platform, then stop worrying about it. That's cross-platform development tutorial #1.
This isn't a "cross-platform development" issue, this is an "older operating systems are missing features that will help us make better software" issue.
In Adobe's case, OS X El Capitan is the first version to support Metal -- this API is much more efficient on systems with multiple CPU cores. Windows 10 is the first version to support DirectX 12, which opens op the capability of using multiple discrete GPUs for rendering tasks on Windows. There is no "cross-platform" or "backwards-compatible" way of doing these kinds of things -- all applications, including your mythical compatibility layer, will depend on the low-level graphics capabilities of the operating systems they use. It's completely unreasonable to expect Adobe to reimplement core OS features just to appease some technological refuseniks who prefer decade-old operating systems for aesthetic or emotional reasons.
And look, I get it, people don't like Windows 10 because they've bought into the hype that it's a "spying operating system". Yes, it sends a list of your installed apps to Microsoft, but they do that so you won't receive Windows Updates with known compatibility issues. And yes, it's measuring how long certain operations take, like opening the Settings app, but they do that so that Microsoft can prioritize performance improvements.
As for Apple, yes, macOS High Sierra has been the worst Mac OS release in over a decade, and macOS Mojave is shortening the leash on supported hardware range for Macs to 6-7 years, and it's removing features that people actually use like Back To My Mac... it's really super-frustrating.
But here's the thing: both operating systems also continue to add very useful programming APIs for developers so that they can continue to improve their software. The next update to Windows 10 is finally adding native Unix-style ptys, for instance, and the console natively supports xterm-256color. Mojave, for its part, is finally implementing the OpenType-SVG font standard, i.e. fonts with colour. Maybe these don't interest you, but there's literally thousands of low-level improvements like these over the last several years, many of which would make your computing life nicer.
But if you don't know about those things, and make personal computing choices based solely on press negativity, you'll never get to learn about, much less enjoy the upsides.