Writers hate to repeat what’s been done before. This is particularly apparent when it comes to dialogue tags (those things that come after a line of dialogue and let you know who spoke):
“The bit after the dialogue is called a dialogue tag,” he explained.
What’s wrong with the above sentence? The answer is simple: the dialogue tag (‘he explained’) adds no value. It’s obvious that whoever’s speaking is explaining something, which makes it redundant to tell readers that things are getting explained (and as discussed before, redundancies are bad). You don’t need ‘explained’ – you just need ‘said.’