I had that thought as well. You would be wide open, exposed, anybody along the river could spot you and if you heard a helicopter or other aircraft coming there wouldn't be much you could do about it. It would be incredibly foolish.
However, maybe not as much at night. I could see them going for it at night. It would still be foolish, but it's possible.
I just don't see where else they would be. It just seems very unlikely to me that these two would be able to completely avoid all detection for almost 2 weeks. They need food and they need water. And if they try to travel they're going to be spotted. So ending up dead in the river certainly provides a logical explanation for the current state of the manhunt.
I will say also that I do not believe they think the game Rust has prepared them for real world survival. The game may show their proclivities, but no gamer is going to think that tapping a button would prepare them for real world survival. I just don't see it.