As a writer, you're not really asking this question, are you?
Yes, because as a writer, I can recognize the devices and narrative structures that other writers use in their work and the reasons that they use them. You can argue all you want about how the characters
could time travel in theory, but it only happens
if the writers want them to. And the fact that the writers so quickly and cavalierly wrote off time travel as an option in the first act of the season premiere couldn't be a clearer telegraph that they do not want this to be a time travel story. What interests the writers, what their attention all season has been focused on, is building the post-Burn world.
In series fiction, time travel resets are done to preserve the status quo of the series. The post-Burn 32nd century
is the status quo now, the focus of an entire season. Therefore, erasing it with time travel would be the opposite of what time travel is usually used for as a story device. It's not just about what
can happen in a story, it's about
why things happen in stories, what purpose the storytellers intend them for.