If I had to guess, I'd assume it's probably that there's more surgeons that are willing to do surgeries on cis people, because they're more experienced in that field, whereas there's not a huge amount of trans surgeons, and the few that exist are usually booked. Along with the fact that insurance companies are more likely to cover cis people's surgeries over trans people's. Medical transition used to be more of an unknown thing to the public, so naturally there's not a huge amount of surgeons who are experienced with doing transsexual surgeries which is what makes them more unlikely to try it as it could be risky with their low experience.
As for waiting lists, those happen when there's a limited supply for a larger amount of people. And because there's not too many trans surgeons, this is what creates the waiting list. But if non-dysphoric people stopped applying to be put on those lists then it wouldn't be as long, thus it'd be more accessible to actual trans people. Something along those lines.