Maybe I'm reading too much into the situation, but it's my impression that "cooperat[ing] with FCC, internal investigators" means talking with them without support from counsel and union representatives. Or at least, sharing more than they advise. I expect that it takes some time for them to negotiate on his behalf with those investigators. And in the meantime, saying nothing is the best option.

Also, "cooperating" implies some shared goal. Such as discovering the facts of the matter. But that's very likely not the case here. These investigators arguably need someone to blame, and the likely candidate is pretty clear. The "button pusher" needs to focus attention on underlying problems, and that's a huge burden for a drone. Others with expertise need to do that.