No, they don't put DP on because every $ of hardware they fit to the TV needs to provide value. DP requires a large board component that may need manual handling, circuit traces (+ decoupling) and silicon on the chip to interface. It then requires software support in the stack and that needs testing/validation.

The percentage of people who will actually use DP to connect their TV vs HDMI is tiny. Even people who do have DisplayPort on their monitors will often times connect it with HDMI just because it's the more familiar connector. I spent a decade working in that area and we literally were debating about spending cents on devices that retailed for hundreds, or thousands. The secondary problem that drives that is that ~90% of TVs sold use the same family of chips from MStar, so even if you wanted to go off-track and make something special, you can only do it from off-the-shelf silicon unless you pay a fortune for your own spin of the silicon. If you want to do that then you better commit to buying >1m chips or they won't get out of bed.

HDMI forum was founded by mostly TV manufacturers, they're not interested in constraining the market in that way. It's all just been market consolidation and making TVs cheaper through tighter integration.