Further, somewhat more speculative thought:

A totally causal universe has the potential to have an initial state (including the rules of its time-evolution) that is extremely simple (low Shannon entropy), as compared to a causal-but-with-some-exceptions universe. As Eliezer points out, it also requires vastly less computing power to 'run'.

It therefore seems perfectly reasonable that universe-simulators working with non-infinite resources would have a strong preference for simulating absolutely causal universes - and that we should therefore not be terribly surprised to find ourselves in one.