I saw the list of rest stations that are (re) opened.  I don't know how many are still closed, or which ones.  I don't know the answer to your question - why all are not open. I would suspect it would have something to do with potential people-to-people contact in physical facilities. 

???

BTW, do you typically use rest stops in PA.....on a routine basis?

I am just curious why someone in Ontario is concerned about rest stops in PA.