You have hit on one of the most controversial and confounding problems: why don't doctors educate their cancer patients about lymphedema? Over my years at the NLN I discovered a thread of similar responses: 1) the doctor doesn't "believe" that lymph node removal causes lymphedema (usually with the qualifying statement "All of the evidence is anecdotal" or something similar, though research exists and can be accessed); 2) the doctor believes that such a small percentage of people develop lymphedema, why scare the patients anymore than they already are?; 3) the doctor is afraid that if s/he educates the patients about lymphedema, they will be so afraid that they won't undergo the potentially life-saving surgery.
Those are the main three. Educating the doctors is key. I know the NLN offers biennial conferences for professionals - we just have to get all of the doctors to attend!
Take good care,