HDMI exists because the corporations behind the HDMI group are the ones that make most of the TVs and dvd boxes. So by pushing HDMI they get to use it for free while the competitors have to pay extra and are at a disadvantage. Nvidia and AMD are not on the HDMI group which is why on pro and enthusiast hardware displayport is pushed much more. My current gpu has 3 displayport and 1 hdmi.

On the tv side, the benefits of displayport are less important since most users are not watching 4k 144hz content and hdmi is now capable of playing 4k at 60hz. So hdmi is not only pushed by the corporations but is also the most convenient option the users want since all of their other hardware uses hdmi and it works fine.

Honestly I think GPUs should drop the hdmi port entirely and ship with a displayport to hdmi cable which works fine because displayport gpus also support hdmi and dvi over the dp port.