X is dependent on you using a Operating system supporting X. Ssh can be used across all operating systems, even as an Android app. Sometimes that can be useful.
There are X servers for most major operating systems, including, AFAIU Android. For OSX it's XQuartz (either native or XTools), for Windows, MingX11 and I suspect WSL, as well as various proprietary tools.
I'm not arguing that X11 is more streamlined than remote SSH (or tmux!) in a terminal / console. But it is far more available than you might think.
Android is an interesting use case. It would probably be mostly useless to SSH from an Android if the TUI ecosystem wasn't so prevalent.
You probably also refer to Windows and MacOS, but that just corresponds to another type of difficulty (Xming, Xquartz), it doesn't make it inherently worse/impossible.
I'm not arguing that X11 is more streamlined than remote SSH (or tmux!) in a terminal / console. But it is far more available than you might think.