So far as I can tell, Genie wishes are not up to interpretation of the genie and they are just using the magic to let the wish come to be, so the alignment wouldn't matter if so, since as summoned creatures, they are forced to do as you ask. The biggest reason I can think of for the preference though is that Noble Djinn have only a 1% chance to come into existence, and while anything can be summoned no matter how rare, it just feels strange calling lots of them to yourself