The subject is moving. It is "i" because it implies the action "to or toward." It would be "ma" if the action were implying a stationary action "at or in." For example, Going to Honolulu versus Working at home. "Hele i Honolulu." "Hana ma ka hale." We can re-arrange the action and get the same result. Working in Honolulu versus Going Home. "Hana ma Honolulu." "Hele i ka hale." The difficulty arises with modern teaching that allows "i" and "ma" to be interchangeable. Oftentimes, that is true. But sometimes the switch creates a weird visualization. For example, I am cooking in the kitchen. "Ke kuke nei au [i/ma] ka lumi kuke." One cannot be cooking toward the kitchen, so the natural tendency is to choose "ma." But I believe "i" is also an acceptable choice only because its meaning is understood. Some folks are traditional over this and some folks are contemporary.