The difference between the way doctors and lawyers look at standard of care depends on what they consider worthy of a standard.
Physicians typically believe a reasonable standard of care includes customary practices. Meanwhile, malpractice lawyers are more likely to think that care and practice are separate (although they may overlap). This difference is because medical malpractice is a field of personal injury law. Personal injury law has the reasonable person standard regarding negligence—if a reasonable person would have done something, then not doing it is negligent, and vice versa.
Doctors are cautious about using a reasonable standard. Physicians know there are always risks and complications with any procedure. By avoiding a reasonable standard, they’re avoiding an implication that complications were negligent.