She's 15 is the good reason. She's a child.
The whole purpose of having children be Protected People is to withhold their identities so they won't be to be grilled, or shamed, publicly.
The same WADA Code that will punish her for the violation (despite her age) is also supposed to protect her from public scrutiny. You can't demand that one part of the Code be upheld but disregard the other.
The other skaters deserve answers, but it doesn't have to be right now, it doesn't have to be in the form of an Olympic press conference, it doesn't have to come directly out of Valieva's mouth, and it doesn't have to be on camera.
A press conference right now would be nothing but a public pillorying of a kid.