It was a tiny cessna. The president doesn't need to be briefed on every tiny detail at the moment it happens. What was telling him about it supposed to accomplish anyway? Nothing would have changed at all, except his bike ride would have been interrupted.
Kinda like reagan: "If our planes are shot down, yes, they'd wake me up right away. If the other fellows were shot down, why wake me up?"
I would have wanted to be told though.
Hindsight. Not all details are available at the time the intruder is detected. Besides, a Cessna 152 filled with C4 could obliterate your neighborhood and then some. And the President's wife was in the White House and potentially in danger. He should have been told. I sort of want to be told if my wife is rushed away in a limousine somewhere.