The problem is that Wayland just isn't a compelling alternative for many people, so they don't move. For me, I see no benefit because I got used to avoiding HiDPI and don't have a mixed-DPI workspace. For some bizarre reason they made each compositor implement input-handling separately, so for example artists might have to switch compositor just to use their tablet of choice. And worse yet, some people with input accessibility needs are just going to get straight up locked out of libre computing. See https://nocoffei.com/?p=451 for one example.
I have used only HiDPI monitors with X11 on Linux for about a dozen years and it has always worked perfectly.
However I use XFCE, where you can set directly the DPI values of the monitors, so that everything will work fine. I have heard Gnome users complaining about problems with HiDPI, but those are not caused by X11, but by a bad Gnome UI for desktop settings.
So HiDPI is not something at which Wayland is better than X11 and there is no reason to avoid HiDPI. At a higher DPI, OTF/TTF typefaces are rendered much more beautifully and reading becomes more comfortable.
I do not know if Wayland has any advantage at mixed DPI, because I have rarely used such configurations.
In the end Red Hat failed to kill off X11. Let's see what happens next. The
GTK devs already rejected patches for maintaining the toolkit further for the
xorg platform, following their "GTK5 will no longer support x11" agenda. Would be kind of great to have a universal GUI toolkit that would
work rather than have toolkits controlled de-facto by private companies who just willy-nilly throw out support for this or that platform at their own selfish discretion. Though,
someone else now helps maintain gtk2, though most of the patches are in regards to
fixing bugs, ensuring that it can be compiled and so forth. https://git.devuan.org/Daemonratte/gtk2-ng
Wayland was started 18 years ago. When it was conceived, X11 was 20 years old. In 2 years, we should probably start talking about replacing Wayland with a modern display server...
In all seriousness, it is another stark reminder why you never rewrite from the ground up. Especially when you're replacing a foundational technology like the display server. In the same time Microsoft reworked their display driver model twice without requiring a single change from application developers. The Linux world doesn't have that many application developers, we should not be asking them to continually chase newer and newer APIs. A rolling stone gathers no moss.
Oh no, not this again. The design of Wayland started 18 years ago, but the stabilization happened 14 years ago, and the _convincing_ across the ecosystem obviously happened way later than that.
I would put the year closer to 2016, when distros started to consider Wayland as an option.
Everything "sucks" (has problems) the ways in which X11 "suck" are very well documented and understood, and there are few, if no surprises.
Sure, major version revisions that break the previous API exist. But in my experience there's a new one every couple of years, like branches on a tree, the main trunk will never change.