It heavily depends on the reason for being in therapy, but a lot of times what people do get out of it is a different perspective on themselves and the world around them. It’s not a cure, it’s a series of plans/strategies to handle those feelings in non-destructive ways. It’s about understanding where their issue stems from, sometimes it’s just an imbalance of brain juices, sometimes it’s something to do with their past or upbringing, or education. If it’s the second one, therapy can help those people explore those parts of their past to understand the reasons why they are feeling the things they are feeling and how to mitigate or better handle those feelings.
Others have explained it fairly well too, I think you’ve got a decent enough handle on why therapists are a thing.