It's the fear of not knowing what to do and of being sued.
Surprisingly enough GPs aren't trained as First Aiders. I was on an Emergency First Aiders course last week and the tutor was telling us that she often has GPs on her courses because they're not taught First Aid during their training in hospitals.
Many countries have a Good Samaritan Law which makes it a duty to give help or rescue and, provided that the "Good Samaritan" does their best, they cannot be sued for wrongful action. This law doesn't exist in England as such, but in Scottish Criminal Law a special defence can apply when a stranger altruistically helps another in distress. So long as the requirements of the rescue are met, proportionality etc, then the "rescuer" has no liability.