Do you know why it doesn't feel helpful? Is it possible you are being encouraged (which could feel like pressured) to stay to help you get to a place where it would be helpful?

For example, if a person is holding back, that makes therapy feel unhelpful. That can also can be felt by the group and therapist, so they might encourage the person to stay so they can find their voice. So, rather than quit, they would encourage a person to stay and discover how it can be helpful. Explorieng the desire to quit can uncover some very useful stuff

If you want to end, tell them you are and thank them for their concerns.