My Guess: (SPOILER, dude.)
Keeping Dave and the rest alive always fails because of the traitor among them. And both Roswell and Thanatos knew this. They can't do anything as long as the traitor among them is hidden. I played the DEAN Route first and there was one very disturbing vision when Dave was bleeding running through the Wood (day24) but Dean (while holding a gun!) found him, saying prett coldly something like: So it's you. Instead of "I finally found you!"
On the real Day24 Dave experienced two vision of his Dad while bleeding: The second was obvisoiuly Tyson. The first Dad-version however walked away too fast for Dave to keep up, meaning the first Dad Illusion was potentially Dean who found Dave first but abandended him because he was part of Memphis gang. I also suspected Dean being the potential murderer of Berson because Dean is left-handed. If Dean is the traitor, it also makes somewhat sense for Roswell to kill Dean on Day6; not only to trigger Dave's capabilities but also potentially killing a traitor , if Dave fails with his first password. Basicly a WIN or "at least the traitor is dead" situation. What speaks against Dean being the traitor is Thanatos behaviour towards him. "Keeping his options open".