Ujiko spent his time daylighting as a medical doctor and turned children into nomus when they appeared to have useful quirks. We can see this with assuming the winged nomu who briefly kidnapped Deku was also the child with wyvern wings in the beginning (who never shows up again). The reason why Deku is still Deku and not a nomu is because he of course did not have a quirk.

Damn that doctor always crushes hopes. Whether you are a hero or a villain you will be a failure to him nonetheless.