To be fair, Kul Tirans along with Junk Gnomes are the most unpopular races in WoW due to their appearance. For most people the race has fundamental issues even without the lack of customisation as they are basically just hairless Pandaren. With dev resources being sparse enough as is, customisation options for a dead race are probably at the very bottom of the pile.
Yep. The development team could add thousands of customisation options to Kul Tirans and Mechagnomes but they just aren’t anything other than an extreme niche.