This is OP again. As an experienced classroom teacher, I understand those saying: no parents. You need somebody on your page, and independent enough to be helpful. Volunteers could be a burden, or worse, a gossipy interloper. However, the parents who understood how to support activities, were gold. I remember you folks for years.
I also remember years when school librarians were cut and school libraries descended into chaos or were carried by volunteer parents.
The Post had an article a few months ago about the sorry state of a PG school with an under-resourced library. It is not the school I posted about, but it’s another example of how a lack of resources-including personnel- hurts kids.
If you refuse qualified offers for help, and the teachers recognize the volunteers are qualified, but the principal bars the door, the principal is hiding something. Most likely their own incompetence.