Why were eunuchs allowed to serve in a variety of occupations in the muslim world?

The reason why Eunuchs could serve in a variety of occupations in the Muslim world because they were viewed as more dependable and manageable. 
The majority of Eunuchs were in the service of mosques during the eighteenth century in Mecca, they were the preferred male slave choice for consumers, because they posed minimal security risk at the harems, in the palace and in the domestic affairs of ordinary Muslims.

The holy roman empire.