Because it's potentially an abortificant. This is one of the most proven and widely used drugs for autoimmune disorders, and also used for ectopic pregnancies and cancer treatment.
https://www.arthritis.org/about-us/news ... ate-access
For a lot of people with autoimmune disorders it's the only drug that works. Ectopic pregnancies are invariably fatal without treatment. And we all know about cancer.
And this is one of many widely used drugs that red states are banning, and that doctors and institutions in blue states are preemptively cutting off just in case, like absolute cowards.