The problem is that if widespread desktop Linux adoption is the goal, then the tools for amateurs aren’t going to cut it. Not even close. Tools that professionals use need to be available and they need to work like they do on macOS and Windows, it’s pretty much that simple. I think Darktable is fine for me tinkering around with my amateur photos. If I were a professional using it daily I’d probably hate it.
As much as we wish it wasn’t true, most people don’t really give a shit about their OS. It’s the logo that appears when they boot up their computers to work. What they do care about is having their tools available to them, if they can’t use the Adobe Suite, Pro Tools etc (and no, WINE is not a practical solution for most of these people) then Linux of any flavour is functionally useless to them. It’s for this reason that smug people saying “just switch to linux lol” as if it’s an actual solution whenever a Windows user complains about some rabidly anti-consumer bullshit that Microsoft is forcing onto them annoys the hell out of me.
It’s changing somewhat now, but it’s why you’ll find that a lot of people in the creative industries traditionally stick with macOS, because for a long time the options for those professionals were just better on that platform and people tend to stick with what they know.
On the other side of that coin, you have software vendors looking at the single-digit market share that Linux on the desktop “enjoys” and coming to the fairly reasonable conclusion that building packages, fixing bugs and providing support for myriad different distros just isn’t worth the headaches it will inevitably cause for them.
Classic chicken and egg problem.