Why not increase the number of Flight Data Recorders and add jettisoning capability? With some Flight Data Recorders gone unrecoverable during crashes , what's the argument for not changing their locations, like wings or engines?

Given their utility after accidents, why not increase the redundancy even more by placing separate boxes in each engine for example.

I understand that military aircraft have jettisoned Recorders  that signal their location for recovery. Could this option be considered with Jettisoned Engines even before the crash in case of Extreme Load or excessive vibrations ?
The simplest argument to me is that no location on the aircraft is particularly special when it comes to locating black boxes in this sense. The recorders that aren't found are either in exceptionally remote locations or underwater - I don't see anything special about an engine that makes it more likely to be found than the wreckage of the fuselage.

No matter where you place them, there are going to be circumstances where they can't be found.