Also, if one is positing that there's a civilization advanced enough to spend time making sims, one can reasonably argue that they will be capable enough such that any of them could program the sim themselves, in a way similar to how anyone can program a Basic program to say "Hello World!" in our world.

Our civilisation is advanced enough to spend time making computer games. This doesn't mean the average person can make a computer game.

Anologously, in the hypothetical highly advanced civilisation, it could be that it's considered basic to program a halo-equivalent, but only very few would be able to program a worldsim.