"Postmen do not work at post offices, but on the streets."
Translation:A postások nem a postán dolgoznak, hanem az utcán.
Because English is weird. :)
The languages approach these general statements differently: English talks about the sum of all post offices and streets, hence plural; and Hungarian goes more with the general principle of the objects.
Hungarian has a general aversion to using the plural, too. You could also say "a postás here if you want.
But then how would one translate to Hungarian "the postmen do not work at the post office, but on the street" -- if it would be the same sentence in Hungarian, then I don't see why we need the current sentence, which honestly doesn't make any sense in English and is impossible to guess without getting it wrong first.
It would be translated the same.
The English sentence does make sense to me. It talks about postmen in general, and in those cases English likes to pluralise everything. But you're right, it isn't needed and I'd recommend reporting your suggestions of alternative translations. :)