Are they cis guys who are attracted to trans women but don't know how to process that in healthy ways so it comes out in transphobia? Are they just transphobes and they get their jollies out of being straight up sicko creeps? Or something else entirely? I'm just curious as to what makes them tick.
Fetish for chicks with dicks. Nothing more. That is all they see in the trans person they are chasing, when relationships do happen due to the poor judgement of the trans person they tend to become incredibly manipulative and abusive if/when full transition surgery becomes on the table as this would remove the thing they like. They don't really give a shit about the trans person as a human being, they're a sexual fetish and nothing more.
There are probably a bunch of other factors involved. Trans women tend to overcompensate a lot to seek gender affirmation which makes them uniquely manipulateable by someone that understands the things they want, they tend to hyper-feminise in an overcompensating way, they tend to be open to being hyper-submissive in an overcompensating way. Etc etc. A lot of trans people grow out of the overcompensating later on but yeah, it makes them targets for a lot of stuff.