We know there is gravity because apples fall from trees. We can observe gravity in daily life. If we could throw an apple to the edge of the universe, we would observe it accelerating.
Adam RiessUntil the 1990s, there were few reliable observations about movement at the scale of the entire universe, which is the only scale dark energy effects. So dark energy could not be seen until we could measure things very, very far away.
Adam Riess