And I'm an expert on what it's like to have people fuck with your head. It never leads to anything good. Besides, if we end up with the resistance, what do we do next? Erase more memories? We're already in a temporal war. If the bus needs us to fix a timeline, we'll worry about it then.
And not knowing how they escaped can impact their decisions too. Everything impacts our decisions. Picking what lies we tell them impacts their decisions. The ripple effect is from Back to The Future. Modern science is based on the theory of relativity that states that time travel is impossible (shows you what Einstein knew). Whatever book you are reading took the term from a movie.