I am not an expert in Kung fu, but having seen some tutorials it seems to me that it's useless in a street fight because of the following two reasons.
First of all the stances are ridiculous, for example the eagle stance is one of the worst stances I have ever seen, you basically stand on one leg in a squat position, why would anyone want to fight like that? The problem with the stances is that they require a lot of training just to be able to sit in the stance, they are very uncomfortable and waste a lot of energy for no particular reason.
Second, the other problem is that many moves require a lot of energy and in my opinion it's easy to miss, many moves are acrobatics essentially and I see no reason why to do this unless it's for a show.
Please note that I am not trying to insult Kung Fu practicioners but rather trying to understand how this can be useful. Also I am referring mostly to animal style Kung Fu and similar styles like wushu, shaolin Kung Fu etc. I am not referring to wing Chun and Jeet kune do, which I Know are very useful for self defense.
So, having said that, can Kung Fu be useful for self defense?
Finally! A question on a Stack Exchange site worth asking 😉Is Kung fu useful for self defense?