There are already a lot of excellent answers already describing how the two compare in balance etc. Her I would like to advocate the a single technique instead of comparing the two in general. This technique is often forgotten, because it is not allowed in most sports-based martial arts: the kick to the groin, which is of course a low kick. It is the single most effective technique in self-defense (after running away). Here are some of it's advantages:

1. Speed: it requires nothing more than a snap kick with the lower leg, which is faster than any kind of roundkick or roundhouse kick, even slightly faster than the higher aiming front kick. The only kick that comes close in speed is a kick to the knee, but that requires more force, which brings us to the second point.
2. Damage per power: even if it is only a light kick that hits correctly, the damage is fatal to the extent that any opponent (unless he/she is a crazy shaolin monk who practices this sort of thing...) will at least cringe, which sets up for further attacks/punches. So even if the opponent is significantly stronger this will be the kick of choice.
3. Reach: Due to not requiring a lot of power, one can train to make this one of the highest reach kicks in your repertoire.
4. Required precision: Depends on the distance, but as long as the kick ends up between the legs, it is not very hard to hit.
5. Lack of fatal damage: A factor that is not to be underestimated in self-defence is that unlike for kicks/punches to the head, the opponent can easily recover from a kick to the groin on the long term. This is important since in unclear legal situations (i.e. it is not obvious that you were the defender), you would not be sued for having used inappropriate measures for your defense. Especially in Germany beating up an attacker too hard can get you in quite a bit of trouble.

How does this answer the question?

Why not prefer low kicks?

You should, in fact you should prefer a very specific kick as elaborated above. This is for real self-defense situations. Of course if you are fighting in a bar kicking to the groin might count as cowardly.

Is there a situation in a street fight where high kicks would be the best choice?

There are, specific examples are opponents that charge at you, against which the best defense is a step to the side and a high/medium-high round kick. Of course if the situation is a 1vs1 fight rather than an actual street self-defense situation (the distinction is that in the latter there will usually be not much facing off, it is just an attack and a defense maybe with some follow up) then you should use all the tools at your disposal and have a fight strategy. If high kicks are part of that depends entirely on you.

There are already a lot of excellent answers describing how the two compare in balance etc. Her I would like to advocate the a single technique instead of comparing the two in general. This technique is often forgotten, because it is not allowed in most sports-based martial arts: the kick to the groin, which is of course a low kick. It is the single most effective technique in self-defense (after running away). Here are some of it's advantages:

1. Speed: it requires nothing more than a snap kick with the lower leg, which is faster than any kind of roundkick or roundhouse kick, even slightly faster than the higher aiming front kick. The only kick that comes close in speed is a kick to the knee, but that requires more force, which brings us to the second point.
2. Damage per power: even if it is only a light kick that hits correctly, the damage is fatal to the extent that any opponent (unless he/she is a crazy shaolin monk who practices this sort of thing...) will at least cringe, which sets up for further attacks/punches. So even if the opponent is significantly stronger this will be the kick of choice.
3. Reach: Due to not requiring a lot of power, one can train to make this one of the highest reach kicks in your repertoire.
4. Required precision: Depends on the distance, but as long as the kick ends up between the legs, it is not very hard to hit.
5. Lack of fatal damage: A factor that is not to be underestimated in self-defence is that unlike for kicks/punches to the head, the opponent can easily recover from a kick to the groin on the long term. This is important since in unclear legal situations (i.e. it is not obvious that you were the defender), you would not be sued for having used inappropriate measures for your defense. Especially in Germany beating up an attacker too hard can get you in quite a bit of trouble.

How does this answer the question?

Why not prefer low kicks?

You should, in fact you should prefer a very specific kick as elaborated above. This is for real self-defense situations. Of course if you are fighting in a bar kicking to the groin might count as cowardly.

Is there a situation in a street fight where high kicks would be the best choice?

There are, specific examples are opponents that charge at you, against which the best defense is a step to the side and a high/medium-high round kick. Of course if the situation is a 1vs1 fight rather than an actual street self-defense situation (the distinction is that in the latter there will usually be not much facing off, it is just an attack and a defense maybe with some follow up) then you should use all the tools at your disposal and have a fight strategy. If high kicks are part of that depends entirely on you.