Also in Dinah's case pretty much everyone from the Trinity on down, including her husband and his boyfriend, Hal, pretty much acted like she wasn't in charge - undermining her from the start. She was in a no-win situation. One could make the case Vixen could make a good head for the next JLA since she was basically the only one from Meltzer's JLA team who hasn't at some point bailed (even lying about her powers to stay on it).
As for Peege, I always thought the Old Guard gave it to her because of her generation she's been the constant one on the team, the one who thinks of the JSA as her family, so they probably figured she deserved it.