I have been told (but not confirmed) that is mandated by the HDMI mob. If you want HDMI on your TV, it cannot also have DP.
Which is kind of funny. At least, to my mind this has associated HDMI-only with the budget option (TVs), and DP with the premium tier (monitors).
This can only be true for consumer-grade stuff. Even then I just guess the manufacturers kind of cheap out.
I have a dumb-ish Samsung Hotel TV / commercial TV at home. It has DP.