[FpUser]

>"First, supporting desktop/mobile software can be hard"

I have Windows desktop software (my product with about 40,000 customers) that I support and I would not call it any harder than maintaining for example backend C++ servers I make for my clients.

>"What happens when Apple removes an API that your program used?"

No idea about Apple as I do not develop for their platforms but my yet another desktop software (uses DierctX 9 and DirectShow) that did release in 2003 and abandoned sometime in 2008 as the revenue had decreased still works like a charm.

>"Programming languages move on and you're stuck with an IDE highlighting things as bugs or that won't launch your program because it isn't compatible"

That DirectX program I just mentioned was developed in Delphi 7 (I use Delphi and / or Lazarus to develop desktop applications). This Delphi 7 still runs and compiles this software on my Windows 10 machine. Latest Delphi which I have compiles it as well with no problem (just checked).

So yes in theory you are right, in practice (as much as it concerns my products) it is however totally irrelevant.