Use the HDMI port when I connect my MBP to my 4k Dell display.
When I visit relatives, when I am in a meeting, and when I am doing event production.
For that last one I really do not want to use a dongle. I've seen those overheat and fail. Never seen an HDMI port on a Mac just stop working.
As others have pointed out, having an HDMI frees up your other TB ports to do real throughput without preserving bandwidth for the display.
That you think only 10% use the port only proves you don't get around much.
HDMI ports and cables are more ubiquitous than ethernet now.