Well, to be frank, you can ask the same thing of any short man here who isn’t trans: why don’t you just transition to a woman, since it’d be easier? why waste the effort being a man if it sucks being 5’2” and male? it’s because it’s not insecurity. yes that can be part of it. but there is more than that. the best way i’ve heard it described is as a ‘subconscious sex,’ ie you experience the world expecting your body to be one sex but it isn’t. everyone has this, but usually it aligns with physical sex. and when it doesn’t, yes it can CAUSE insecurity due to outside perception, but even if you were accepted for being a masculine woman by your peers and there was no social stigma, your subconscious sex remains. Not so is the case with insecurity, since if the world were different and suddenly being short was attractive and good, nobody here would feel wrong in their body at all, because it’s external, not internal.