I'm not a therapist, but as I understand it most therapy isn't about suicide, and doesn't carry suicide risk. Most therapy is talking through problems, and helping the patient rewrite old memories and old beliefs using more helpful cognitive frames. (Well, arguably most clinical work is convincing people that it'll be ok to talk about their problems in the first place. Once you're past that point, the rest is easy.)
If its prompted well, ChatGPT can be quite good at all of this. Its helpful having a tool right there, free, and with no limits on conversation length. And some people find it much easier to trust a chatbot with their problems than explain them to a therapist. The chatbot - after all - won't judge them.
My heart goes out to that boy and his family. But we also have no idea how many lives have been saved by chatgpt helping people in need. The number is almost certainly more than 1. Banning chatgpt from having therapy conversations entirely seems way too heavy handed to me.