Its not easy to spot wreckage from the air. Hours of staring at white waves wondering if one of them is something more than a wave. Grey clouds, grey seas, and grey aluminium.
If you want to find wreckage at sea, paint the planes fluoro yellow. White and grey are almost camouflage in poor conditions.
And thats before you consider how large the search area is, and the delay before the search started in the Indian ocean.
Its not always easy to even spot ships from the air. There are numerous WW2 examples of planes missing ships (and even convoys) when they must have passed almost overhead. Pilots from the Ark Royal launched torpedoes at the Sheffield when they believed they were attacking the Bismarck.
Im not at all surprised at the lack of wreckage. Maybe if the fuselage had been breached and lots of bright things spilled out. But a few control surfaces or even a couple of wings would be hard to find, even if still afloat at the time people started looking.