If there's one conference that would schedule a televised expansion event in early-evening to announce it has a new media deal and will not expand, it's The Big XII.
I don't understand the criticism. The expansion decision is a national story. The decision to not expand is every bit as newsworthy as expansion. They should be trying to spin this into a display of stability and power from the current members. Not that that will matter as whatever the Big 12 does will be mocked by national pundits because it's cute and hip.
But to casually release a statement announcing no expansion would be met with more ridicule. At least with the press conference, the Big 12 can (hopefully) go into further detail about the process, reasoning and decision.