Why do people get so angry at the apparent fridging of the mothers of the three heads of the dragon given that all their fathers die violent deaths? It’s not exactly gendered death, there’s no disparity.

All of the women involved die in childbirth, which is inherently gendered. Moreover, some or all of these conceptions (depending on the theory under discussion) lacked consent, which is also gendered. 

Whereas all three of the fathers die deaths that are not gendered at all. 

That’s the disparity.