... monitor stand. .... you can say it is that expensive because of all of the intricate engineering and R&D ... But what's up with the $199 VESA mount adapter? Isn't that just a machined metal plate with some plastic and no moving parts? How do they justify that price?
It is not a simple metal plate.
"... With a similar design to the magnetic connector on the Pro Stand, it can be placed and secured quickly and easily using the included Apple-designed tool. ..."
https://www.apple.com/pro-display-xdr/specs/
All the 'intricate engineering and R&D" that went into the Stand's attachment costs is right here also. A little more since the four "arms" coming out of the center all have to be precisely milled to fit into four different vent holes on the back and appear to also have some magnets.
Over the last approximately 1-1.5 year there have been some rants bouncing around the Youtube and forums about how Apple used "cheap screws" that strip easily on the VESA mount for the iMac Pro. Well ... this version appears to be basically screw less. So no "cheap screws" that came with
$79 iMac Pro VESA Kit . Couple the "no screws" and the weight of the panel enclosure is about the same and it won't be more affordable than the "cheap screw" version if it is engineering to be very secure ( don't want $6K panel falling down because mount was 'weak'. )
Over time someone will probably reverse engineering the Apple tool and the basics of the design. It is far more than simply stamping out a metal plate and pre drilling some screw holes in it. There doesn't appear to be any screw holes in the monitor case for semi-standard mount holes to align with.
So it becomes a question of spending about 3% more for a $6K display to Apple or betting that "Woo's product chop shop" clone actually works in this highly specialized monitor ( and different from all of their stamped out solutions. ) In most places the sales tax is going to be higher than 3% and users will get far more immediate, direct utility out of the mount than the sales tax.
If the mount proves to be flakey then that would be a point of contention. If it is a bit over engineered that most of the rest of the specs of the monitor then that probably won't happen.