Because, apparently, medical training for doctors relating to endo is still based on research undertaken 50 years ago and much of that original thinking is now considered flawed/out of date by today's leading lights - but still remains the basis of general medical training. Hence you still get gynaes saying pregnancy or hysterectomy cures endo.
It does feel like a minefield out there of mis-information and consultants with differing degrees of skill and knowledge and treatments. This is something you certainly don't appreciate when you first get referred to the local 'general gynae' by your 'general' practitioner.
The experts believe that Endo (which is generally of the peritoneal cavity) and Adenomysis (endo like growths in the uterine muscle) do not have the same origin and do not necessarily migrate one into the other and so are separate conditions; albeit ladies who have peritoneal endo, do sometimes have adenomyosis also.
The majority of general gynae consultants (who are not necessarily endo experts) still try to treat endo by drugs which only temporarily supresses it (inducing chemical menopause which is not an attractive prospect for a young person - or an older one at that!), or the birth control pill / Mirena which is opposite to menopause and mimics pregnancy (great relief from painful periods tho but does nothing to tackle the endo itself), or recommend a hysterectomy and removal of ovaries, (which will not sort widespread peritoneal endo, only deal with adenomyosis). I am guessing that the drug option maybe useful where ladies are suspected of having adeno and who have not completed their families and need pain control until after they have completed a family. Where endo is peritoneal, it still makes sense to have the endo excised rather than leave it if it is widespread.
GPs tend to refer you to whoever has the title 'Gynae' at the local hospital - but they all have such a wide range of specialisms and some really are 'general' with a broad spectrum of knowledge but not specialising in particular. Best to see someone who has chosen to become an endo expert with up-to-date knowledge and enhanced skills relating to endo. Excision surgery is the most satisfactory way of treating periendo at the current time.
I can also recommend the following books:
Stop Endometriosis and Pelvic Pain by Dr Andrew S Cook (top USA Endo Surgeon Consultant)
100 Questions and Answers about Endometriosis by by Dr David Redwine (retired top US Endo Surgeon Consultant (acknowledged as world leader in the field)
All very best wishes to you . Frances x