They do it to make sure you actually need an urgent appointment as these appointments are very limited. Could be 30 urgent appointments a day for a catchment of 10,000 patients. They want to check you actually require a same day appointment or if they can book you in for a normal appointment at a later date, or even signpost you to a more appropriate place for care such as the pharmacy, dentist or an urgent care centre. Try not to worry about it, they will do it for everyone.