The problem is that channers complain, but do not do productive things like file PRs. So problems that matter to channers will remain unresolved.
If you want something done right, do it yourself. Commercial software is no exception to that.
>why Linux on the desktops fails to take hold.
Linux fails to take hold because it doesn't come preinstalled on laptops, and because it doesn't have the critical market share to take over. Basically nothing to do with file pickers.
The ideal use case is just using drag-and-drop behavior from the file manager, instead of implementing the file manager twice. The reality is that products like Windows have shaped people into thinking about the desktop in a certain way, and linux has limited leeway in reshaping those ideas (including their idiosyncrasies like file pickers).