More often “cis person primarily trying to get with trans people” is about power, from what I hear. Trans people are disproportionately in positions where they can be easily exploited or abused, e.g. outing someone can be used as blackmail, an abuser could withhold HRT or trash clothes, trans people might not have learned how to date safely as their gender, many trans people are broke and in poor mental health and could easily become reliant on someone, things like that. On top of this, trans people are also often particularly desperate for approval from cis people, because of the extent to which we’re regularly othered by most of society. This creates the idea in a lot of cis men that if they’re unsuccessful with cis women (generally because they’re creeps), that trans women are “easy”. This often mixes with the whole trans fetishization thing, too.
There are of course a number of other reasons why cis people might find themselves primarily dating trans people, too. Another common and very depressing reason is that the cis person perhaps isn’t actually cis, and really just wants to live vicariously through sy partner’s transition, and maybe “borrowing” a few things from thon, as well. There was a Reddit thread I once read with a full typology of different types of trans chasers, but I can’t find it now. There are men and women chasers, straight and gay chasers, you get the picture.