"These stores too are closed, and empty."
Translation:Ezek az üzletek is zárva vannak és üresek.
Zárva, nyitva, and many other -va / -ve forms in Hungarian basically function and behave as adverbs. They don't take further endings (like plural or accusative), and they can't function as a predicate by themselves. They have to modify a verb.
(You can derive such a -va / -ve from practically any verb, although the result may not be something that's as commonly used as zárva and nyitva are.)
Because it is in the plural. It used to be that you would be able to say "zárvák", but that is not valid anymore. Remember how an adjective gets the plural if it is behind a noun? This is kind of the same idea, except you can't put this particular word in the plural. Hopefully somebody can explain the theory behind it.
Basically, "zárva" is derived from the verb "zár". Its role is mostly the same as the third form of a verb in English: "close" - "closed". "It is done", "it is closed", "it is read", etc., they are all created similarly. They cannot be put in the plural. Instead, you add the plural "vannak".