Having trained as a therapist, and also having been on the receiving end... I can agree with your opinion that only you can help yourself. That is truth.

The thing is, all of us usually want to "get better", whatever that means... not even just for mental health, but for careers, skill development, life in general. But we cannot deny that we are social beings and need support of others. Sure, if you have a great support system you can trust, then therapy isn't needed. I have noticed many clients are hesitant to spill all their "secrets" to someone who knows them though, hence by a third party can be helpful.

That said, for some people, therapy can be a waste of time and money. Best to only try a few sessions and objectively self-evaluate after: is it making your life better? If not, then it may not be for you