Here is my attempt to rephrase Vladimir's comment:

Consider a possible world W that someone could simulate, but which, in fact, no one ever will simulate. An agent A can still care about what happens in W. The agent could even try to influence what happens in W acausally.

A natural rejoinder is, How is A going to influence W unless A itself simulates W? How else can A play out the acausal consequences of its choices?

The reply is, A can have some idea about what happens in W without reasoning about W in so fine-grained a way as to deserve the word "simulation". Coarse-grained reasoning could still suffice for A to influence W.

For example, recall Vladimir's counterfactual mugging:

Imagine that one day, Omega comes to you and says that it has just tossed a fair coin, and given that the coin came up tails, it decided to ask you to give it $100. Whatever you do in this situation, nothing else will happen differently in reality as a result. Naturally you don't want to give up your $100. But see, Omega tells you that if the coin came up heads instead of tails, it'd give you $10000, but only if you'd agree to give it $100 if the coin came up tails.

Now consider a variant in which, in the counterfactual heads world, instead of giving you $10,000, Omega would have given you an all-expenses-paid month-long vacation to the destination of your choice.

You don't need to simulate all the details of how that vacation would have played out. You don't even need to simulate where you would have chosen to go. (And let us assume that Omega also never simulates any of these things.) Even if no such simulations ever run, you might still find the prospect of counterfactual-you getting that vacation so enticing that you give Omega the $100 in the actual tails world.