If reality is a simulation, then why is evil allowed to exist, or why did our creators let evil exist?

I know that the point of having a simulation is so that we can learn about life, but why is it more likely to be in a simulation with 'real' characteristics rather than one where everything is utter happiness? Why didn't our creators make infinitely more simulations where people are just happy all the time?

Of course this brings us to the question of whether you can know happiness without pain. If reality is a simulation, couldn't it be possible to make people happiness with only the memory of pain (or just knowledge of pain) without actual pain? I would think so.

What do you think?