Because dragons are gigantic? and would not work as a race?
the thing is how they will do that kind of race, they can go in the route of
"those are descendant of dragons and a race of their own" like basically dragonborn from D&D or do with the material we have, Drakonid by example are humanoids who turn into dragon-like races, the humanoids could spend eyars with dragons and be affected by their magic or simple perform rituals with dragon magic and turn with drakonids.
The dragonmaw clan in outland does literally that, there is orcs whowith dragon magic turn themselves into drakonid, Zuluhead by example, prior chieftain of the clan, can turn back and forth into a netherdrakonid form.
In azeroth, Dragonmaw clan use different types of dragons on their ranks, and use the dragon magic deeply, they even threat wounds with dragonblood, so, putting dragon magic on their own veins, if you see their models, they are a strange gray and have glowing yellow eyes, prob showing the dragon magic influence, it would be perfect to turn the whole clan into a draconic race.
The race would basically be like worgens, human->worgen, but orc->drakonid.