Why? if a women gets her tubes tied does she still get a menstrual cycle.

Ovulation still happ: A tubal ligation does not stop a woman from having a menstrual cycle. A woman continues to ovulate and the uterus continues to respond to hormonal changes. A tubal ligation does not stop that from happening.

Ovaries still work: Tubal ligation just prevents the oocyte (/egg) from travelling down the tube / sperm from travelling up the tube and fertilization from occurring. Ovaries would have to be removed to see significant change in cycle.