Some combination of: HDMI consortium is backed by numerous large TV manufacturers and movie studios, DVI lacks audio support, HDMI already had a lot of traction

Some combination of: HDMI consortium is backed by numerous large TV manufacturers and movie studios, DVI lacks audio support, HDMI already had a lot of traction by the time DP was released, DP initially lacked HDCP support, HDMI supports much longer cables than either DVI or DP.