Gender is a load bearing brainworm for capitalist society. Capitalists need stratification, having a gradient of various degrees of precariousness for workers to experience that would push them into accepting a worse deal for selling their labor. Gender is clearly one of the primary ways to achieve this: an absolutely incredible amount of domestic labor is performed without compensation by women every day, and society would fall apart if it wasn’t. The rigid structure of the patriarchy is a key feature of this system, which means that trans people represent a clear break in that logic; if AFAB individuals can just choose not to be subjected to gender-based exploitation, it starts to rip the whole thing apart. Equally, transfeminine people represent another break in the opposite direction. The patriarchy is more or less incompatible with the existence of trans people, at least without significantly transforming itself.
I wanna add that the way I formulated it is incomplete, or at least too partial to the functional perspective that someone who wishes to preserve the status quo would have. Obviously trans people don’t just “choose” their gender, it’s much more complicated than that. But I think it’s worth looking at things from this lens to understand why the billionaires in particular are recalcitrant about gender.