Because, IMO, not due to anything that's been said by LE at this time, but because Denise was said to be in the home, there's a high chance that there was sexual assault in the victimology. That's not something usually released when the daughter is still missing and could possibly still be alive, I don't think.
I believe it would not extend her chance of survival at all.
I hope this makes sense. I know what I mean. It's like not saying " kidnapped" but " endangered missing". They want to use the LEAST INFLAMMATORY terms possible for that slim chance that Jayme is alive so the abductor doesn't panic and kill her.
We know the chances are high that at some point, when the autopsies are completed, we will know more of what happened to each parent. If I was holding the press conference and was asked the question about where Denise was found, and what was believed to have happened inside the house prior to James's arrival and the progression to gunshots, I'd say: " There's time for this info to be told, and it will be forthcoming as soon as the forensic autopsies are concluded and correlated with our crime scene processing data, but now, they are looking for the little girl first and foremost".