This may be pedantic, but I'm baffled that PBS page doesn't mention every PBS station is available for free over the air.

PBS is "free to air", meaning it can be redistributed verbatim within the US with minimal delay without permission from the parent company.

As a result, they have no incentive or negative incentive to advertise that other stations carry their content.

Content created by PBS and its member stations carries a copyright notice and cannot be legally redistributed without permission.

Not so. The local PBS stations do fund raising / pledge drives. It's definitely in PBS' interest to push people to local PBS stations.

Or did I misinterpret your point?