Because it is irrelevant, just like the police announcing a missing women was struggling with HRT. Neither of these points are relevant, to the general public, what is relevant is that a child was murdered and a women went missing.
Bringing up the fact she was trans almost feels as though you are victim blaming, and other threads have done just that, "if they weren't trans they wouldn't have been murdered", these types of remarks start to remove blame from the perpetrators to the victim... The bottom line a child was murdered, that is the important point, along with the importance of the discussions above in this thread around "how do we reduce knife crime"... Do we "blame the victim and say if they weren't XXX this wouldn't of happened", or do we look at ways to address the socio-economic factors behind the perpetrators actions, such as supporting the activities of organizations like youthendowmentfund.org.uk/ and having discussions around what leads people to think that carrying (using) a weapon "is what you should do".