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

It is quite a common phenomenon that couples or for that matter anybody arguing to shout. I think that by shouting they just wish to prove themselves correct and other person wrong. They need to understand that shouting does not prove anyone as wrong or right.

Because they are hurting inside or they always want to be right. They don't apologize and some think the fighting would make them close when they make it up. That's not how they cope with fighting/arguing

Its the nature of duality. Where the extreme passions of love exist, there is an opposite flow of the nature of passionate discourse.

Because couples usually love each other and thus they have great expectations from each other. The reason they yell instead of talking quietly is because sometimes ego creates this problem and yes we cannot forget the fact that we know that saying things loudly would create more impact on the other person which is what both of them want. And yes, scientifically couples that fights moderately frequently are bound to stay together for a longer time

Emotions are not easy to control when you are arguing with someone u care about the most. Sometimes emotions just take over and you become overly loud or expressive. Does not mean you are overacting just means that you care so much to show that you do.

Because they feel like they aren't being heard. And they feel like there point has not been made.

People often forget it isnt not one person versus another, but both parties versus the problem. We assume the role of right or wrong and create tension.

Because they need to make pressure on some words, they need to express their anger, they want to make sure the other party knows what they're talking about, they want to embarrass each other, and there are countless other different reasons

It could be a wat of releasing the stress they have on themselves helping the suituayion calm down after all the screaming

They tend to have a lot of pent up problems and frustrations. They might not even realize they are yelling. Think of it as a dam that eventually overflows. The water gushes and flows, slow at first but eventually a torrential wave.