These are simulations of BEING on Mars, not the far more cramped and dangerous process of getting there. They still go wrong. Less than complete perfection in space means death. It is like getting to heaven. Only God can make you acceptable to be with Him. One cannot do all that is required.
Why do they not simulate the process of GOING to Mars? That has to happen first. I can only conclude that it is because NASA and the private companies involved are not serious about going to Mars in the first place, and are only using the idea to get people to support them and give them money.