DP/mDP is a much more versatile port to have on a dock of any type (TB3 or vanilla USB-C) compared to HDMI. Mainly because it can be changed via small adapters into most/all other main display types (DP/mDP, HDMI, DVI, VGA), and even split into two/three lower res ports (i.e. a 4K DP 1.4 port can be split into two/three 1440p/1080p ports using various adapters**).
Canât help on the tech reasoning dock makers have on this, unfortunately. (Though Iâm guessing pricing targets, and the consumer nature of HDMI, perhaps.)
âŚMuch like the deep tech reasoning on why no long OPTICAL TB3 cables have been forthcoming for nearly 3-years (since the first TB3 Mac appeared; late 2016 MBP)?
EDIT: Though apparently Corning are finally releasing optical TB3 cables!
It could be something as dumb as what happened to radios a long while back. An available commodity chip that does the work and everyone uses it because designing one that does better or more isnât cheap. Differences in the feature sets of products would be due more not enabling all of the possibilities allowed by the chip.
That said, OWC does have a better usb-c dock with more usb A ports than average plus mini displayport (includes a displayport to hdmi adapter), but itâs $120, big, and needs to be plugged in. It also only has one usb-c port, so no daisy chaining.
That must be the bulkiest dongle ever shipped. Looks like itâs designed to eventually break the receptacle on that dock. But seriously, at $120 youâd probably be better off buying a real TB3 hub (at least in Mac land). Sure, thatâll cost another $30 more, but it will also be substantially better overall.
I looked at usb-c hubs when I first got a Macbook in 2015. There wasnât much around then and I ended up with a Satechi dock which has worked well. Also at the time I think it was pointed out that usb-c is not intended for daisy chaining and is limited with the number of usb-c ports on a hub. That is why most usb-c hubs only have multiple usb3/A ports and one or no usb-c. It seems the usb-c committee did not regard this as important.
In any case, the above discussions remind me of the early days of Thunderbolt (1) - very difficult to find a product with all the features. This was disappointing after the good olâ days of Firewire docks.