HDMI connectors cost a lot of money to the HDMI licensing authority. This payment is very painful if you have a small quantity of shipments. DisplayPort is free. And as others have pointed out, you just need to buy a cable.
Wouldn't display over USB-C solve this as well?
It looks like this does support display over USB-C - the tech specs have a snippet saying that you should use DP over USB-C so you see the BIOS.