Just target Windows, business as usual, and let Valve do the hard work.

Alternatively, RemObjects makes Elements, also a RAD programming environment in which you can code in Oxygene (their Object Pascal), C#, Swift, Java, Go, or Mercury (VB) and target all platforms: .Net, iOS and macOS, Android, WebAssemblyl, Java, Linux, Windows.

We might take it for granted but React-like declarative top-down component model (as opposed to imperative UI) was a huge step forward. In particular that there's no difference between initial render or a re-render, and that updating state is enough for everything to propagate down. That's why it went beyond web, and why all modern native UI frameworks have a similar model these days.

The answer to maintaining a highly functional and stable OS is piles and piles of backwards compatibility misery on the devs.

You want Windows 9? Sorry, some code checks the string for Windows 9 to determine if the OS is Windows 95 or 98.

Competition. In the first half of the 90s Windows faced a lot more of it. Then they didn't, and standards slipped. Why invest in Windows when people will buy it anyway?

Upgrades. In the first half of the 90s Windows was mostly software bought by PC users directly, rather than getting it with the hardware. So, if you could make Windows 95 run in 4mb of RAM rather than 8mb of RAM, you'd make way more sales on release day. As the industry matured, this model disappeared in favor of one where users got the OS with their hardware purchase and rarely bought upgrades, then never bought them, then never even upgraded when offered them for free. This inverted the incentive to optimize because now the customer was the OEMs, not the end user. Not optimizing as aggressively naturally came out of that because the only new sales of Windows would be on new machines with the newest specs, and OEMs wanted MS to give users reasons to buy new hardware anyway.

UI testing. In the 1990s the desktop GUI paradigm was new and Apple's competitive advantage was UI quality, so Microsoft ran lots of usability studies to figure out what worked. It wasn't a cultural problem because most UI was designed by programmers who freely admitted they didn't really know what worked. The reason the start button had "Start" written on it was because of these tests. After Windows 95 the culture of usability studies disappeared, as they might imply that the professional designers didn't know what they were doing, and those designers came to compete on looks. Also it just got a lot harder to change the basic desktop UI designs anyway.

The web. When people mostly wrote Windows apps, investing in Windows itself made sense. Once everyone migrated to web apps it made much less sense. Data is no longer stored in files locally so making Explorer more powerful doesn't help, it makes more sense to simplify it. There's no longer any concept of a Windows app so adding new APIs is low ROI outside of gaming, as the only consumer is the browser. As a consequence all the people with ambition abandoned the Windows team to work on web-related stuff like Azure, where you could have actual impact. The 90s Windows/MacOS teams were full of people thinking big thoughts about how to write better software hence stuff like DCOM, OpenDoc, QuickTime, DirectMusic and so on. The overwhelming preference of developers for making websites regardless of the preferences of the users meant developing new OS ideas was a waste of time; browsers would not expose these features, so devs wouldn't use them, so apps wouldn't require them, so users would buy new computers to get access to them.

And that's why MS threw Windows away. It simply isn't a valuable asset anymore.

It's not a moving target. Proton and Wine have shown it can be achieved with greater comparability than even what Microsoft offers.

If you make a piece of software today and want to package it for Linux its an absolute mess. I mean, look at flatpack or docker, a common solution for this is to ship your own userspace, thats just insane.

What are some examples?

Windows kept logging down the system trying to download a dozen different language versions of word (for which I didn't have a licence and didn't want regardless). Steam kept going into a crash restart cycle. Virus scanner was ... being difficult.

Everything just works on Linux except some games on proton have some sound issues that I still need to work out.

Good operating systems should:

1. Allow users to obtain software from anywhere.

2. Execute all programs that were written for previous versions reliably.

3. Not insert themselves as middlemen into user/developer transactions.

Judged from this perspective, Windows is a good OS. It doesn't nail all three all the time, but it gets the closest. Linux is a bad OS.

The answers to your questions are:

(1) It isn't backwards compatible for sophisticated GUI apps. Core APIs like the widget toolkits change their API all the time (GTK 1->2->3->4, Qt also does this). It's also not forwards compatible. Compiling the same program on a new release may yield binaries that don't run on an old release. Linux library authors don't consider this a problem, Microsoft/Apple/everyone else does. This is the origin of the glibc symbol versioning errors everyone experiences sometimes.

(2) Maintaining a stable API/ABI is not fun and requires a capitalist who says "keep app X working or else I'll fire you". The capitalist Fights For The User. Linux is a socialist/collectivist project with nobody playing this role. Distros like Red Hat clone the software ecosystem into a private space that's semi-capitalist again, and do offer stable ABIs, but their releases are just ecosystem forks and the wider issue remains.

(3) It hasn't change and it's still bad.

(4) Docker: "solves" the problem on servers by shipping the entire userspace with every app, and being itself developed by a for-profit company. Only works because servers don't need any shared services from the computer beyond opening sockets and reading/writing files, so the kernel is good enough and the kernel does maintain a stable ABI. Docker obviously doesn't help the moment you move outside the server space and coordination requirements are larger.