If emergency, go to A&E.
If not emergency, then go when polyclinic is open.
Problem is, a lot of people don't know what is emergency to the extent that they are willing to wait. At least in the emergency department, someone is looking out for the patient, even in waiting area.
Is diarrhoea an emergency? What if the patient is very old or very young? And it's at night and the caregiver cannot differentiate between sleepiness and drowsiness? Objectively, one can assess but if you are wrong, your loved one dies. So it's either GP or AnE.
Day time. Your colleague has fainting spells. He says he is ok. Do you call an ambulance, ask him to see doctor (take time off) or just continue working since he says he is ok?
If you are medically trained or confident, you might say ok, won't go ane. But members of the public might just want to be safe. At least some medical attention. And at night, only AnE is available.
Day time, it is possible for more to go to see GPs or polyclinic but some are not confident or the patient is non ambulant.
Two examples
Bedridden parent.
Someone with very bad abdominal pain at the roadside. You are passerby. Either you escort him to GP (and now you are responsible if he faints along the way) or you call an ambulance and settle the issue.