There's a wide spectrum of responses people can have to a breakup. Anger to the point of violence is naturally low in most modern societies, but it does exist.

When you have that breakup moment in person, you force a lot of emotions to flood them all at once. Often, they thought things were going well. This creates a strong sense of rejection, hurts their self-esteem, and puts them immediately on the defensive. It can also trigger a fight-or-flight response, and manifest as anger.

Ghosting flattens the curve. Over the course of days or weeks, the ghostee more gradually recognizes and comes to terms with the fact that the ghoster is no longer interested in them. This often happens without there being a flashpoint moment to set them off.

It's still rude, but I absolutely see the value in it