8ball
Decolonise colons!
Usually when we want to find out why transphobes are transphobic, why homophobes are homophobic, why racists are racist, why sexists are sexist, it's so we can use that knowledge to change society so people don't become transphobic, homophobic, racist, or sexist. So yes, perhaps it is useful to understand why trashpony is transphobic. It would help us move forward to a better world.
IMO some transphobia arises from a fear that resources that feminists have fought for to redress patriarchal oppressions could be co-opted by men if the only barrier to accessing those resources is identification.
Edit: though this kind of co-option could also be seen as a threat to trans women