This is because it is not actually a property. We can add it using advanced queries though.
#+BEGIN_QUERY
{:title "scheduled"
:query [:find (pull ?b [*])
:where
[?b :block/scheduled _]
]
:result-transform (fn [result] (map (fn [m] (update m :block/properties (fn [u] (assoc u :sched (get-in m [:block/scheduled]) ) ) ) ) result ) )
}
#+END_QUERY