I think it's mostly about the fact that MtFs have been having public attention for the longest time...'status quo is god' or however TVtropes put it. XD ---But yeah, the news is about handing out scoops, and if a topic's unfamiliar then it's harder for people to gulp down, and if the topic is not distressing it's not as alerting and provocative for people to look into. It's certainly distressing for a person to be in trouble and be FtM, but it's hard enough for people to take the idea 'tomboy' seriously, let alone the idea of a genuine man with physically feminine birth. The idea of male-towards-female crossdressers (When not involving taking up other-sex benefits) and stuff have really embedded themselves in history, so people are more familiar-like with MtFs. (keyword 'familiar-like' considering the obvious ignorances) So if it's going to take too long to clarify transexual FtM there's "no point" in their eyes.
That's, just what I think...
(Edited for slight clarification on the crossdresser part of my post)