And you're not the first to assume that. Thing is, if they die, we not only lose any hope of access to the Door that brought us here, our food and power supply goes with them. [They could probably make a go of it for a while, but Rey would rather not be stuck on this planet if she can help it. The cave was better than this.]

That doesn't account for those who don't actually want to go back to where they came from, either.