Killing off the people that support you doesn't seem like a smart way to stay in power. I guess they assume there will be enough new converts to replace the ones they lost?
Well, there also seems to be concerns over testosterone levels & fertility. Combined with attempts to reduce birth control & abortion, and you come away with an expectation they intend to breed their way out of losses (returning again to the eugenics overtones). Someone was also recently quoted as saying measles outbreaks "are the cost of doing business".
It's a death cult. I know that's an inflammatory way to phrase it, but I genuinely think it's the only accurate diagnosis. The regime doesn't have some deep strategic logic for how children dying from polio will benefit them, they just don't care so much about death in general and don't understand why we would.