Are some works now purely of historical interest only?
We have to study Aristophanes' Lysistrata for Drama, and I can honestly see no reason why anyone would bother staging it. Whilst Greek tragedy has been terribly influential on drama and prompted some great plays, Greek comedy (there is only one playwright's works surviving but still) just isn't funny. The translation is terrible- it reads like a bad Carry On film- and aside from that, it's boring. There isn't a plot and there's too much formal verse and convention for anyone who isn't a historian or theatre buff to find funny. Theatre's moved on, people have more sophisticated tastes, comedy's moved on.
The only thing it has to recommend it is an anti-war message but there are far better plays with that.
Can you think of any literature that now seems irrelevant?
My copy of Lysistrata....
is a reprint or copy of the famed one illustrated by Pablo Picasso. I also have some nice copies of The Frogs and The Birds. I haven't looked up the translator of the latter two, but Lysistrata was translated by Gilbert Seldes, probably in the 1930s. I have no problem with the older translations. In fact, when I read Homer, I prefer the translation in verse by Alexander Pope, rather than a modern free-verse translation.
The poster who says that Aristophanes is not relevant to the modern world is probably too young to have valid opinions. He should grow up a bit before subjecting others to his opinions. It is one thing to ask about the Greek playwrites, but another to state an invalid opinion which will probably change with age.