Left That Way 〜てある

The subject takes は or が, never を, even though a verb like 作る is normally transitive and would take を on its object. Once てある is attached, the sentence shifts focus from the action to the resulting state, and the thing affected becomes the topic, not the object.

てある and ている can both describe a resulting state, but てある always implies someone’s intention behind it, while ている with an intransitive verb just describes what’s true, no one’s purpose involved. 窓が開いている just says the window is open, maybe the wind did it. 窓が開けてある says someone opened it on purpose and left it that way.