As Reynolds said, his mum was properly sick. Properly sick people need caring for on the way to hospital. That's what ambulances are for - one crewmember drives, the other cares for the patient. If Tom was driving and his mum's condition got worse, he wouldn't have been able to do anything. (And besides, the fact she was taken to the ambulance in a carry chair suggests she couldn't manage to walk out by herself). The calls Tom complains about attending are those for people who have no medical need for an ambulance, it sounds like this certainly wasn't one of those cases.