Photoshop exists on macOS, which is a *BSD. If something already runs on *BSD it's quite simple to port it to Linux.
But they just won't do it until it becomes used enough
But they just won't do it until it becomes used enough
Which is close to trivial if you're mainly using macOS APIs.
Of course Adobe probably has a lot of platform-agnostic stuff but which wasn't that straightforward to port but I'm pretty sure the UI and system stuff is still mainly using Cocoa.
I'm not even sure the macOS version would be necessarily that easier to port than the Windows one (then again there is probably not that much .net code in their tools)