I'm inclined to believe that most trannies aren't real trannies, they don't actually have gender dysphoria but rather they're grifters who are either groomers, fetishists or attention seekers. The groomers are self-explanatory, the fetishists are caused by the mass adoption of porn, and the attention seekers are a result of social media like Twitter.
The real trannies with actual gender dysphoria though, I'm not totally sure. If we're talking the old trannies of yesteryear, before the 2010s when they became widely recognized, I don't know what the cause of their gender dysphoria could've been a result of.
The new trannies of today though (which is the majority of them), for many it's likely due to the confusion of identity presented with the mass spreading of identity politics and the propaganda associated with it, which is ultimately messing with their brains. Some of them are also just being groomed into it, unfortunately. Most new trannies are young and impressionable, so this makes sense.
It's tough because there are two main "camps" within the trans movement, and of course many sub-camps within them.
The first is the ROGD girls with a laundry list of psych problems that get discarded in favor of trans. A lot of things get labeled as "gender dysphoria". Everything from internalized homophobia, to autism, to reactions from childhood sexual abuse, to social anxiety, to BPD, to just being weird or the general awkwardness of puberty before you're mentally ready for it. Once you have labeled this problem as "dysphoria", now you have a solution: just transition and all of your problems will be solved.
The second camp are the malignant narcs who get off on dominating women, the unassailable motte of LGBT, and of course their own sexual desires. Becoming a woman makes that the narc will always have a woman he can completely dominate.
The victimhood narrative of troonery is especially appealing to people who want to garner sympathy, social capital, or emotionally manipulate others. It's a great way to make all of your bad feelings the fault of everyone else.
EDIT: That reminds me, do we have a troon taxonomy somewhere? I could have sworn we did.
As a starting point:
The ROGD Kid: A young teenager struggling with autism, OCD, BPD, childhood sexual abuse, repressed homosexuality, social anxiety, or just awkward puberty who troons out to find relief from the above psych problems, which then go ignored. Typically starts small by declaring themselves non-binary, but eventually fully transitions after their previous identity doesn't relieve their anxiety anymore.
The Predator: Someone who troons out for the purpose of leverage to get women/lesbians to sleep with him, or easy access to confused ROGD kids. The troonery is used as a fig leaf to excuse or obfuscate predatory behavior. Examples: Yaniv, Sapphixy, Labelle.
The Influencer: Someone who troons out for the social capital or for self-aggrandizement. They are women/trans to the extent that they can gain advantage or make money from it. Examples: Dylan, Nora Reed, Clymer.
The Oedipus: Some who troons out due to severe mommy/daddy issues in order to possess/control their missing parent. Examples: Keffals, Jake Alley.
The Coomer: Someone who troons out primarily for the purpose of sexual gratification. Typically failed men who have consumed way too much porn and 4chan. May use trans status to further excuse why they don't have to do anything in life besides keep consuming more porn. Examples: Zinnia, Kevin Gibes.