I guess this was inevitable.
The whole point of public domain is that nobody owns what is public domain.
So somebody makes money out of collecting information on which sites feature Public Domain material.
So, a great number of people volunteer and put a lot of time into finding, buying and collating public material to create the site [and similarly others make other PD sites.] and somebody else can only think about exploiting it for money.
Mormo Zine, not aiming this at you. Good luck with your enterprise.