True you get clues from the beginning that things aren't so dire, but what kind of person would be aware that they are at risk of turning into a horrific monster at some unstated point in the future and not make stopping that their primary goal? Like, sure we see that a bunch of other people have been infected with tadpoles and haven't changed after a pretty long while, and some people would take that as permission to slow down, but we don't have a clear sense of how long the True Souls have been a thing or if it's guaranteed that you're not going to change earlier than they will. You have the equivalent of a ticking time bomb in your brain and you don't have a clear estimation on how long you personally have, that's not all that comforting. When you use your tadpole powers you are even told that your character feels themselves losing something they can never get back. It's still perfectly rational to try and hurry to find a solution.
You don't at the beginning, but you come across two unchanged people who have died with tadpoles in them very quickly, and then you come across several living people with tadpoles in them, and you know they have had them for more than a few days at the very least, because of the events that you've already been told about. So again, it's not like you stop the quest for getting it removed, it's just that you no longer have the sense of "if I don't find a cure before I camp I'm going to change into a mindflayer".
