That’s a good question.
Also, if a male is unable to learn the social skills to socialize with females, it can stunt his personal growth.
Josh socialized with a houseful of females every day.
Moreover lack of socializing with non family females doesn’t cause normal 14yr boys to fondle their 4yr old sisters.
There are a lot of families of similar belief and size in the Duggar circle, it’s not like Josh was never around females at all.