There was a time when Pennsylvania had what was known as Blue Laws. These laws prevented sale of any nonessential items to the public. Businesses as well as the public lobbied to repeal these laws. Most of these laws effected all business on Sundays. Most businesses were allowed to operate on Sunday after these laws were changed,but many businesses close early because it is not cost effective to operate all day on Sunday. Saturday closing early is due to short staffing.
I am assuming you mean Sunday specifically. They used to be closed on Sundays but then opened for limited hours and it hasn't changed since.
I'm guessing it follows the public transportation schedule on Sunday.
I've wondered the same thing
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