That's not a Wayland thing. That's a DE thing in Wayland. This used to be the role of X, but it is not for Wayland. Different DEs may wish to implement different methods for handling this, Wayland steps out of the way allowing DEs to implement their own process of placement.
Except that's not why it doesn't exist, and has even been proposed as a wayland protocol. Wayland doesn't claim "not a Wayland thing", but instead argues that, somehow, this is now simply impossible. Because it only handles rectangular 2D monitors aligned well with x and y axes. They bemoan that by it's nature, it can't be "optional" because if it is possible, then applications will bank on it, and thus "break" when an environment opts out of it. Because it's not perfect, they don't want it at all. All the while neglecting to make an acceptable counter proposal, just closing proposals as either being "inadequate" by failing to address the "what if it's an alien interface" concern, or "over complicated" if it strives to actually cover those hypothetical interfaces.
I'll confess they have something of a point, I was a developer on a project where this was desired, and it was a PITA under X desktop environments. When we requested coordinates, would they be honored, or shifted? Did the WM count including or excluding it's own decoration? What about panels with forced non-overlapping rules that would adjust our geometry? How much of the shift was due to decoration versus panels and what can we expect lower down the screen? What about if there's some scaling being applied and what does that do to our geometry? I'd love for a better solution to exist and would be happy for their "better idea" to be offered, but as it stands it's a matter of letting the perfect be the enemy of the good. Rejecting the imperfect but familiar solution in favor of the perfect solution no one can seem to come up with.
Should we ask the people who pour the blacktop on the highway to also tell us what to set the speedlimit to?
Again, that's not why it's not in Wayland, but let's entertain your line of thinking. It's not that there's a "speedlimit" authority, so it's more like:
-Some group says the speed limit should be 65 mph and puts up a sign
-Another group thinks the speed limit should be 160kph, and puts up their sign too
-Another group thinks there should be no upper speed limit, but a lower speed limit of 80 mph
-Another group thinks that it should be 200 kph, but measured relative to the relative movement of the air instead of ground speed.
So now you have to drive down this road, faced with a dizzying array of rules that are hard to follow and impossible to concurrently comply with, while driving alongside other folks trying to also decide which policies to follow.