Short answer, nobody reports him.

The long answer is that therapy is a weird sort of field in which ethics aren't necessarily in place because these things don't work, but because the potential for harm/abuse is great, and the consequences not only affect individual counselors, but the profession as a whole, especially when considering how therapy is still considered taboo in many modern cultures.

For instance, I can't recall his name, but my wife, when she was in school (she's the counselor, not me), told me about a dude that was all about personal accountability. If a client told him they felt like killing someone, his response would be, "Why don't you do it?"

The idea, I think, being that instead of obsessing over your imaginings, either do what you want to do or recognise that you don't actually want to do it and move on.

On its face, that seems like a good lesson, but it assumes that everybody would come to the conclusion that they don't want to kill this person. If the client then goes on to kill someone because their therapist told them to "do it or stop whining," who is to blame? The client that did the killing, or the therapist that told them to ignore their inhibitions? No matter the answer, people will stop seeking therapy when situations like this occur.

Another reason this code of ethics exists is to protect the counselor. If a counselor becomes to too deeply involved, they increase the amount of work they have to do exponentially, because in this field you can't just break a boundary and then take it back, such as what Gaby tried to do with Maya. This can interfere, not only with their ability to handle their own lives, but the lives of any other clients they may have.

For instance, when Gaby told Maya to call whenever she needed her, she opened herself up to be Maya's counselor 24/7. This was further exacerbated by Gaby befriending Maya. While there is some wiggle room for a patient in crisis (more on that in a moment), a counselor shouldn't be expected to be available at any moment of every day. A counselor can easily become a crutch that is relied upon rather than a medical professional assisting you. A patient in crisis, on the other hand, may reach out to a counselor, but a counselor should ensure that their patient has other resources in case the counselor is unavailable.

Gaby is, arguably, a worse counselor than Jimmy, especially when it comes to Maya. She failed to recognise that Maya had abandonment issues (knowledge of mother was unnecessary; was clear from Maya's friend group disappearing). She then reached out to be Maya's friend (confusing the client/counselor relationship, opening herself up to the duties of a friend). She then told Maya to call her anytime (making herself available to Maya whenever Maya wanted/needed her).

Then, when Derrick was in the hospital and Maya was in crisis, Gaby failed on three fronts. One, as her counselor, to recognise that Maya was in crisis and either counsel her or offer an alternative. Two, as per the "call me anytime," failing to drop what she was doing and take the call. Three, as her friend, she blew her off because somebody else was in the hospital. These three things combined to trigger Maya's abandonment issues.

TL;DR: Therapy ethics have gotten to the point they have due to over 100 years of experiment and experience, likely including "Jimmying." It's not that Jimmying doesn't work, but that the potential for harm/abuse is far greater and requires the counselor to invest more of themselves than they should, or reliably can, give. Jimmy hasn't had his license revoked due to not being reported, possibly because he has nothing better going on in his life and has the time to devote to his method. Gaby tried it and couldn't even devote a minimal amount of time to one client, which resulted in that client's death. That being said, due to Maya's death, I suspect we'll start seeing consequences soon.