ObservedObject not working when getting data async for view - swift

Question

Using StateObject allows my view to rerender correctly after getting data asynchronously but ObservedObject does not, why?
I have two swiftui views. First is the root App view and the second is the one consuming an ObservedObject view model.
From the root view I create a ViewModel with a firebase object ID for the second view and pass it in. When the second view appears I'd like to then send a request to Firebase to retrieve some data. While the data is being retrieved I show a 'loading' screen.
When I use ObservedObject my second view never rerenders after the data is retrieved. Using StateObject though fixes the issue but I'm not sure why.
I think I understand the differences between ObservedObject and StateObject having read the docs. But not sure how the differences apply to my case since I don't think the root view should be rerendering and recreating the ViewModel I created there and passed to the second view.
There is a Login view which forces the RootView to rerender after login but from what I know, the SecondView still shouldn't be rendered more than once.
https://www.avanderlee.com/swiftui/stateobject-observedobject-differences/
RootView
#main
struct MyApp: App {
#ObservedObject private var userService = UserService()
init() {
FirebaseApp.configure()
}
var body: some Scene {
WindowGroup {
NavigationView {
Group {
if (userService.currentUser != nil) {
SecondView(secondViewModel: SecondViewModel(somethingId: "someIdGoesHere"))
} else {
LoginView()
}
}
.environmentObject(userService)
}
}
}
}
View Model
class SecondViewModel: ObservableObject {
#Published private(set) var thing: Thing? = nil
private let thingService = ThingService()
private let thingId: String
init(thingId: String) {
self.thingId = thingId
}
func load() async {
self.thing = await thingService.GetThing(thingId: thingId) // Async call to firebase
}
}
Second View
struct SecondView: View {
// Task runs to completion but 'Loading...' never goes away.
#ObservedObject var secondViewModel: SecondViewModel
var body: some View {
VStack(spacing: 5) {
if let thingText = secondViewModel.thing {
Text(thingText)
} else {
Text("Loading...")
}
}
.onAppear {
Task {
await secondViewModel.load()
}
}
}
}