That's kinda the point! Well, half of it is. We feel disenfranchised from humanhood every time we try to communicate with non-autistic people, which is most of our daily interactions. There's this feeling of an inch thick pane of frosted glass between us and everyone else, where we can only pick up vague parts of whatever they're saying or gesturing. They of course don't see what they want in our communication because of the frosted glass, but make it our problem because we're the one encased in glass of course! People talk freely and enthusiastically amongst each other, then turn to us and their entire demeanor changes. Clearly, they don't treat us like people, so something about us isn't people-like.
This kind of autistic trauma fueled many things in our life, from kinks to personality to gender, and is the biggest reason we were drawn to it/its pronouns.
In many ways, it's about retaking control. Control over perceptions, control over acceptance, and control over narratives.
Control over perceptions - hearing us referred to as "it" immediately signals that something is off about us. People perk up when they hear it, because usually their only experience with it comes from sci-fi media (e.g. the endless discussion of whether non-humans can achieve personhood) or transphobic tirades. They understand in some way, at least subconsciously, that they should think twice about treating us like any other person, which is good because we're very autisticly queer and queerly autistic. We want you to feel the dehumanizing you put us through anytime we interact.
Control over acceptance - using our pronouns is a very low bar to clear. It should be no different than he/she/they, no different than neopronouns, you should hear our pronouns and use them without hesitation. If you can't handle that, if you can't or won't get over the discomfort of using pronouns you have or haven't heard before, then you're not ready for other, more deviant parts of our identity or someone else's identity. To be an ally, you have to accept all queer identities, not just the ones you find tolerable enough to accommodate. People's genders are none of your business, all you have to do is treat everyone as equals.
Control over narratives - dehumanizing and invalidating the identities of trans women is a regular pastime for terfs and other bigots. They'll call women "it" to disenfranchise them from a womanhood that these bigots have no right to gatekeep. By already not strictly identifying with womanhood, by accepting and leaning into the freak nature assigned to us by society at large, we become less susceptible to these tactics. Of course, it's less about the word choice than it is about the intent and delivery, and this does nothing to actually defeat bigotry, but we find it personally fulfilling nonetheless.
So please, call us "it" the way you call a cute animal "it", the way you describe a beautiful sunset with "it", the way you fall in love with a book while calling it "it". So many beautiful things in this world are its, why not consider us one of them?