I believe you mean the (general) transparency of state? But yes, that's quite great when you're getting stuff together quickly. It's even used for more serious stuff, where immediate mode is a necessity.
The thing is, immediate mode UIs are not really usable, because a widget needs internal state, so a pure immediate mode UI would require the caller to carry around all that state. Obviously that is burdensome, which is why Dear ImGUI hides it for you. But in my opinion, it's a bit of a fraud to call that an immediate mode UI, when it retains a copy of state behind its back.
So basically you are dismissing an existing definition to turn it into your own to say that existing libs are not fulfilling that definition.