You may not see it as abuse of power, but it is considered abuse of power by professional ethical standards. The reason for that is that a client is in a more vulnerable position than a therapist. Much more vulnerable. Not only does it make it more difficult for a client to say no to a therapist than to say no to other people, but it also makes a therapist unable to fulfill their professional duties because a dual relationship wouldn't allow a therapist to be as objective as they should be.

Regardless of how you see it, the professional code of ethics sees it as abuse of power. It's just a fact.