The fewer the number of pieces of wreckage on impacting the water, the lower the chances of discovery. Even a bad ditching in the dreaded 'roaring forties' may only result in a few pieces of wreckage; a wing, a tail an engine, etc., compared with hundreds of pieces from a high speed impact. It's also well outside any expected search area. Anyone planning this is unlikely to have known about the ACARS pings, much less the doppler effects resolving the ambiguity of direction. Finessing the ditching is rather irrelevant to someone planning this. Suiciding prior to impact does dramatically increase the chances of discovery due to the fragmentation of the aircraft, but this does involving guessing the perpetrator's mindset.
The same scenario in other optional ocean regions involves a far greater chance of eventual discovery because of greater radar coverage and much shallower water.