I'm an EMT. When I was first certified, we had to go through a practical test of asking the patient medical history, what happened, allergies, medications, etc. Through the course of the test, we probably asked "what happened" two or three times. I knew the ER would ask again. And again. I thought it was wasteful and said so.
The EMT who was training us explained that stories often change through those multiple askings. My experience confirmed her explanation. As another commenter mentioned, the truth GRADUALLY comes out. Though many people will answer "What's your medical history?" accurately each time, some will change the story based on who is there, how much time they've had to think about it, once they've calmed down, and whether something else you've said reminded them.
"Do you have any medications or history I should know about?" once turned from "No" into "I have a chronic medical condition and take numerous medications for the condition" based on some gentle reminders. "Could you be pregnant?" turns from "No" into "Yes" once family members are no longer within hearing range.
A lot of medical inefficiencies make more sense when the soft squishy human side is taken into account.