Scott Peterson did interviews, lots of them in which he professed his innocence over and over again. And we no know he killed Laci and Connor. So willingness to do interviews to protest innocence doesn't mean much, but leave you open to all kinds of accusations instead, so why would Mark be willing to do that. As I said, everyone in CO knows Dylan is missing and his face is out there.
Where I am, except for the NG item, there has been no media coverage of Dylan's disappearance. Elaine and Cory's last interview did not reach here.
MR has obviously made his decision to cooperate with LE, giving them what they want and just let Elaine and Cory take care of the interviews.