London Plays It Safe?

Several theatres in London, including The National and Donmar, are revisiting the same plays over and over. Phedre, Hamlet, and King Lear seem to be popping up in consecutive seasons.

Does this indicate anything notable about the vitality of new and risky work? What is it about plays like Phedre, Hamlet, etc, that theatres believe audiences need/want to see repeatedly? What do the audiences make of this?