Can you explain why patients with endometriosis have adhesions?

Inflammation. Endometriosis causes inflammatory changes in the pelvis. This causes tissues to become swollen and stick together causing adhesions which may add to pelvic pain.
Sticky Surface. Endometriosis can spread to various surfaces around the pelvic organs. The colon, bladder, uterus, ovaries and tubes move around normally and as they move they touch other things and endometriosis can stick. Endometriosis can also potentially be carried by blood vessels to nearby area, or the surface of the bladder and colon may actually transform itself into endometriosis by chemical signals.