I don't think you'll find a satisfying answer to that question.

Trans-medicalists tend to over rationalize the subjective trans experience and many of them are incapable of separating their own, personal desires from what ought to be for everyone. It's very human to choose a path for yourself and justify it by assuming it's the only "right" way, trans people, while generally much more self-aware than other population groups are not immune to normal human foibles. In fact, dysphoria and other mental health issues related to transness can amplify disordered thinking and lead to outcomes like gatekeeping transness behind expensive, often unattainable, medical interventions.

It's not so much that they are unable to understand, but are unwilling because facing a truth that medical intervention is not a required part of the trans experience can create serious cognitive dissonance, especially if the individual has taken steps on their medical transition they felt compelled to but would not have chosen otherwise.

Folks like that are frustrating and damage the overall efforts of the community to find acceptance. Still I wouldn't hold it against them, we're all only human and doing the best we can with what we have.

Also VERY important, a non-trivial portion of trans-medicalists are either suffering from internalized transphobia or engaging in discussion cynically (such as trolling, or intentionally spreading disinformation).