There's some derived value in the interviewing. It might be to gain insight from an expert in a field. It might be test out interview/hiring practices. For OP

There's some derived value in the interviewing. It might be to gain insight from an expert in a field. It might be test out interview/hiring practices. For OP, it seems like they were never really intent on hiring someone at the time but put out a lowball offer on the chance it would get picked up.