We couldn’t find a commercial jet (MH370). Both, while it was still flying in the air and after it was presumably lost in the ocean. They couldn’t track it in the air nor can they still find its remains after looking for it for so long. This problem is not trivial.
There's a nonzero chance military intelligence agencies of multiple countries know exactly where that plane fell, but none can say anything, because that would reveal the true extent of their capabilities.
The Indian Ocean is both larger and has significantly less traffic than the Mediterranean. And a 777 is about 16x faster than a carrier.
MH370 crashed in the Pacific.
Look at the globe some day from that angle and compare it to the Mediterranean.
Surprisingly, it is much easier to find a big chunk of steel floating on the Mediterranean, knowing where it was a couple of days ago, than a smaller object disintegrated in small pieces under the Indian Ocean. Go figure.
Different times. Now there are thousands of LEO satellites.
Nobody was looking for MH370 while it was in the air. After a few hours, it rapidly became a submarine, which is a type of craft that's well known for being hard to find. In addition to that, it took on its new submersible form in one of the most remote areas of the ocean, rather than in a small and very busy sea.
A commercial jet is both way smaller and faster moving than an aircraft carrier. I suspect this is like saying: why can’t you see the fly in the photo, the turtle is right there!