Hueco Mundo, before Aizen's rule, had nominally been governed by a king, but only in name. In reality, it was still utterly chaotic, without the slightest order. Whenever two Hollows met, they would basically fight and devour each other.
It was only after Aizen appeared, using the Hogyoku to begin Arrancarizing Hollows and establishing Las Noches beforehand, that Hueco Mundo gained a certain degree of order. Stark had come into contact with Aizen under those circumstances.
Stark himself was simply too strong. Ordinary Hollows could not survive by his side; his spiritual pressure was so immense that even when unconscious, it would oppress other Hollows. Thus, he had been terribly lonely in Hueco Mundo, to the point where he eventually split off a clone from his own soul just so he could talk to himself.
It was only after Aizen appeared, established Las Noches, and created numerous Arrancar that Stark no longer had to worry about his unconsciously released spiritual pressure crushing other Hollows to death. Moreover, once Hollows became Arrancar, they no longer needed to devour one another. That was the foundation for order appearing in Hueco Mundo.
Under such circumstances, Stark naturally carried out Aizen's orders strictly. So long as Aizen had not abandoned him, he naturally would not betray Aizen.
"Tier, take them back immediately. Leave this place to me."
Faced with Sakanade, Stark's first move was to have Tier lead the others back to Hueco Mundo. It did not matter if the other Arrancar died, but Tier could not. The Third Espada had been able to hold power in Hueco Mundo partly because of Aizen's orders, but Stark's support had also been indispensable, considering how rarely Aizen had previously visited Hueco Mundo.
Among all the Espada, Stark thought most highly of Tier. Of all the Espada,