As the mighty Warchief of the Horde, how could Zul'ra be drafted just because Chromie said so? Zul'ra had no intention of responding to Chromie, nor was he able to. As Warchief, he could not simply leave Orgrimmar. What if someone took advantage of his absence and attacked the Horde?
Although Zul'ra ignored the summons out of concern for the Horde, little Chromie was quite considerate. She promptly brought out another letter of conscription, leaving him with no choice but to answer the call.
Because Deathwing had joined forces with Ragnaros the Firelord and Al'Akir the Windlord, along with a host of Twilight Forces, to form an army bent on destroying the world, the Twilight Forces were currently being beaten into the ground by the Alliance and Horde. The allied force of saviors had even stormed into the Firelands, preparing to drag out and kill the Firelord.
Since they were going to kill the Firelord, they could not ignore Al'Akir, the other Windlord. Thus, Alexstrasza, in her capacity as the Life-Binder and queen of the Red Dragonflight, summoned Zul'ra to serve as the commander of the Dragon Alliance, intending for him to lead the dragons into Skywall and take down Al'Akir.
With Alexstrasza's written order, Zul'ra had every justification to leave Orgrimmar. He entrusted the government affairs to Rommath, had Cairne Bloodhoof assist in overseeing the city in his stead, and only then departed Orgrimmar for Wyrmrest Temple.
"So, what exactly happened with the election for the King of Magic? Has it threatened the world enough that you need me, the Warchief of the Horde, to step in?" Zul'ra asked Chromie beside him as the glow of the teleportation spell faded.
"Don't talk like you're some once-in-a-world rarity, will you?" Chromie rolled her green eyes at the immensely narcissistic Zul'ra.