Who would have thought we would be back here so soon listening for pingers completely unsuitable for the function we now require of them.....
They are extremely short range (and short lived) and so can only be relied upon for locating the recorders when you are in the right vicinity.
Hopefully thy are close to the section they reportedly recovered a body from. However you would hope they would have heard them if that close. Not much you can do about waves, but presumably non essential ships and aircraft can be kept away.
So maybe they are further away. Or maybe burried in silt. Or maybe they didn't survive intact.