Dunno why people act like something has to be life-or-death for it to be covered. No, trans related surgeries aren't the same thing as emergency life-saving operations... But why is that the comparison we make? There are other things that get covered even though they wouldn't be life-threatening without treatment.
Consider this: Roughly 20% of married couples in US are infertile. Many of them try IVF, which most insurances will cover, and cost about $12,500 per cycle. No one seems to have a problem with this, even though infertility is not a life-or-death situation. I think that, when looking at this example and others, it becomes clear the main reason people object to covering trans related surgeries is simple prejudice/ignorance. I mean, the population of transgender people is pretty small, and then not even all of them get surgery, so the overall cost to cover it would be magnitudes lower than IVF treatments.
I don't have a problem with contributing to something of comparatively very little cost to me, that has a high success rate for the people who seek it out (in terms of happiness after the surgery)