HDMI is less hassle. Everything comes with a HDMI port these days, but a DP port is still more of a proper full Computer Monitor(tm) feature. My work just installed a whole bunch of projectors that have HDMI and VGA as input options. I have no idea where they found them.
Of course sometimes the HDMI fails due to DRM nonsense, so that's also an issue.
I think HDMI only exists because HDMI cartel keeps pushing it for patents profits. There is no real need for it because DP is much better. But since they make HDMI only equipment, we are still stuck with it.
And personally, I had a lot of problems with HDMI in the past. Unlike with DP.
Theoretically some DRM content should refuse to play at full resolution on DP connected displays due to the lack of DRM on the cable. I've never tested this myself, but you often see requirements for things like Blu-Ray players that you have to be running a late model Intel chip, on a supported motherboard, on Windows 10, over HDMI to a supported monitor. Get anything wrong and you've got a 720p picture or a black box.
