Because you can get stuck in your own head and then spiral.

That's a fair point you raise, but no. You can't learn this type of stuff yourself. You need a second person to be a sounding board.

Because you need to be able to voice out the stuff in your head in order to process it. A good therapist should then be able to coach you. That bit, the coaching part, that's what is essential. You could do something similar with a friend, or a lover, or a random person you plucked from the street, but you won't know if that person will be able to ask the right questions to steer you in a direction that helps you. It could even be detrimental for your mental health if it's the wrong questions.

Sadly, the same goes when your therapist is not a good fit for you. And it sounds like the therapist you mentioned was that for you. It's unfortunate someone has to get an appointment to get on a waiting list, then book an appointment, have several sessions before you realize this person doesn't work for you. And you have to go through the whole circus again. But that's an issue of healthcare, not therapy in itself.

Also, I would've personally told that therapist to stop being so creepily obsessed with my tattoos. I'd be there with a specific goal in mind, not listen to their Freudian excuses for being a creep.

Would you care to elaborate? Because I love my relatives but that doesn't mean they're equipped to help me process the shit they put me through.

A therapist has learned to do exactly that, and I expect said therapist to do the job they're supposed to do. I still need to do the emotional processing myself, but they're the one teaching me how to do this. It's also their objectivity that actually helps a lot because they're able to oversee the situation without any personal stake.