Why does couples yell so much when they fight, instead of just talking quietly about the problems?

Anger makes your irrational and wild. The want to be right and dominant against their partners. This is wrong; it is important to be humble and avoid pride.

Yelling isn't by itself a problem. In fact, it may well be the case that talking quietly is not as effective as the reservedness may be holding the respective partners back from disclosing the entire issue or issues. One of the things I have always marvelled at is how the southern Europeans tend to deal with things compared to their northern European counterparts; lots of yelling/screaming/crying but then an associated calmness at having bellowed out their grievances. It is remarkable how therapeutic yelling can be!

I think they yell so much if they pospone the talk for too long. The partners just build up anger but dare not mention it so when shit hits the fan it hits it hard. All the stowed away emotions get released and I suppose that's why.

Yelling all comes from a form of stress. They yell at each other because they feel uncomfortable, and not understood. Try to help them find their source of stress or lonliness.

They get emotionally invested in the fight and take the argument personally and emotionally. Meaning, it is no longer about the options.. it is about who is right.. or the morality of the options involved.. or who is virtuous or not.. or who is better.. or the finances are involved and so you have two people frightened by what could happen if they make the wrong choice and it comes out in "how dare you choose this.. don't you know what this means to our bottom line?" Unfortunately, there are also people who have dysfunctionally learned to like arguing and getting the last word or zinger in on the argument and thus sabotage their relationships, which doesn't help usually, even if they want to keep their current relationship. Basically, it grows away from the actual problem and options at hand. Talking quietly and respectfully is always better. Trying to see the other person's point of view but being honest about what you want, in the shortrun, and in the longrun. Negotiating, unless you are up against a wall in your personal values, and then just being honest about it, and having a partner that will respect that. It is very important to having a relationship that will last over the long haul.

Because they aren't listening to each other. Listening (really listening) is a very surprisingly rare skill. But once you conquor it, it solves so much. It boils down to letting yourself be less important, stop taking yourself so seriously, and letting the other person speak with yourself intent to hear them. Not only that, try to pull even more out of them, rather than interrupting them so you can drive home your own point.

Because they've never learned how to really communicate. It's easier to blame loudly than to quietly ask why, and it's easier to call names than to say, "I feel ...when this happens." People who yell can be taught to communicate more effectively.

Emotions. Also, a louder voice can overpower the points the other is making. It'll be nice if there's a rule between the couple to whisper during fights though :)

as no one listens to each other and its just one way to get their points clear...but actually its a bad idea to do and not healthy for any relationship. Having a peaceful conversation can really help ones mind and feelings change towards their partners.

Sometimes people get caught up in being right rather than resolving the problem, which can lead to raised voices. It is always important to take the feelings of the other person into consideration whenever there is an issue.