The simplest explanation for this behavior is not just a Google Forms survey.
To explain why 75% of people verify their documents well before departure, one must think of risks.
No one wants to miss a flight due to an expired passport; it is a cheap way to avoid stress and last-minute expenses.
It's the same as doing laundry the week before an exam to avoid surprises on the day.
The survey provides figures, but the real explanation is problem minimization.