Well they originated during TOS, and having them be Humanoid was the only way to make them convincing.
My philosophy is if you can’t make truly alien aliens, don’t include aliens in your story. The Trek universe is a largely anthropocentric universe anyway, so it would’ve been a better course of action to have made the Vulcans/Klingons/etc. derivations of humanity and left non-human entities out of the picture entirely.