Why writers replace nouns with pronouns?

If we didn't use pronouns, we'd have to keep repeating the nouns which would make sentence cumbersome and repetitive. Most pronouns are short Words. They help make a sentence smoother and easier to say. When we use the pronouns I, me, and you, we don't need to use our names over and over again.

For example:

My nephews Benjamin, Christopher, and Nicholas are coming to visit me. They will stay for a week. I have some activities planned for them.

The same sentences without using pronouns:

Margaret's nephews Benjamin, Christopher, and Nicholas are coming to visit Margaret. Benjamin, Christopher, and Nicholas will stay for a week. Margaret has some activities planned for Benjamin, Christopher, and Nicholas.