WunderPanda!
Jin had this inspiration ever since he used the broken theme park for the zombies' home instance. Every single monster loved the theme park (including Derpy before he was no longer allowed) despite its terrible working conditions.
Therefore, Jin decided to reward his monsters for their hard work (especially with the whole war) with a tremendous Service Instance to provide them with another place to rest, relax and enjoy. But as he was designing it, he suddenly thought why make it exclusive to his monsters?
Why not open it to the public as well?
This way, Jin could recuperate some losses from building this instance as well as ensure future profits if it turned out to be viable. His customers might even like meeting the monsters they fought in person and perhaps take pictures with them too.