Well, sure, but "people in their life that they talk to" aren't really therapists. They're functioning quite differently - they can have a personal involvement

Well, sure, but "people in their life that they talk to" aren't really therapists. They're functioning quite differently - they can have a personal involvement that a therapist, ethically, isn't permitted to have. The sorts of things someone talks to with their friends overlaps with but is also often quite distinct from the sort of thing a therapist is probing for. There's no direct financial incentive to keep the "patient" coming. And they're making no claim to, broadly, help someone improve their overall mental health - people vent to their friends because it feels nice, not because it's necessarily constructive.