Why is implantation in the endometrium critical for the embryo's survival?

An embryo can only attach to endometrial tissue, even in ectopic pregnancies there is usually a history of endometriosis. however, endometrial tissue is outfitted to sustain and provide a housing unit for a pregnancy, and offers adhesive proteins for the egg to attach to. if no endometrium, then no attachment, then no pregnancy.

Answerbasal cell carcinoma;