The thing with therapist support for teens is that it requires the teen to have to go to their parents and ask to be taken to a therapist (not to mention the cost of the therapist). A teen having an AI bot trained on things therapists do/say and techniques they use could give teens an outlet for issues that they benefit from simply venting or talking out, but aren't serious enough to have to go through all the steps and vulnerability/exposing yourself needed when it comes to asking parents to take you to a therapist.

I am not sure I am thinking about the situation of no support, more like sometimes it is good for a teenager to have advice from a trusted adult in addition / complement to the advice from parents, teachers, and friends, all of them having specific bias. It may not be huge distress situations, but more like getting advice on the daily frustrations and fears of teenage life.

Now, why not therapists ? Let's talk straight here: if you can afford it, that is very nice probably.

I am not sure how a teenager would perceive it though. Here in France, there is stigma associated to going to see a therapist / psychiatric doctor, especially for young people (like not being able to manage your own mental health). I think this stigma is unfair as many people have indeed problems and later in their life get mood-altering drugs (I think we are world champions in France for that).

Also, this would be a significant expense that would need to be arbitrated against other activities (sport...), holidays, saving from the studies...