Check out www.DisplayPort.com for more info.
My two cents from a guy that used to work with Chinese factories designing AV equipment: they do not need to.
There is a cost to using the chipsets (royalties) that support such quality output. The other cost is space. If a board designer is out of space, he can switch to a chipset at a higher price that offers such features.
In a laptop, space is at a premium and choosing a more expensive chipset to put on the motherboard makes sense in 2024.
In a desktop space is not such an issue, but sometimes heat dissipation is an issue. So they use a larger connector (space) rather than a usb 3.1 or Thunderbolt connector since they can.
Everything is a balance, from heat to space to cost. If the volume isn’t very high on a production run, then the cost will be high.
Noted, although the laptops seem to have made the transition about 5 years ago. The DP enabled USB-C ports ARE showing up on newer desktops. Possibly the proliferation(!) of USB-C hubs with HDMI output helped drive that?
And still... the lack of expansion cards with “DisplayPort” enabled USB-C outputs is a bit of a mystery. I’m guessing that somehow the desktop motherboards typically didn’t support such expansion cards without a lot of wizardy in the expansion card?