The main reason that endometriosis leads to infertility is that the condition alters the anatomical structure of the pelvic area. It is often found that there are extensive adhesions around the ovaries and fallopian tubes, which can lead to blockage or twisting of the fallopian tubes. This can cause abnormal movement of the fallopian tubes, impacting the transport of the fertilized egg. Additionally, in patients with endometriosis, the pelvic environment is also found to be poor, and some women may experience abnormalities in ovarian function, mainly manifesting as ovulatory disorders. These are all reasons that lead to infertility.