The recorders already to work really well for the purpose they're designed for.
The "bad actor in cockpit" plus "unexplained disappearance" scenario, for which they're not designed, simply doesn't happen often enough to be worthwhile worrying about.
Short version: flight recorders aren't broken, they don't need "fixing"
Long version: imagine you were to propose a major redesign to your employer's systems to attempt to diagnose unaccountable failures which based on historical data happen 0.00000018% of the time[0], what would be the response?
The recorders already to work really well for the purpose they're designed for.
The "bad actor in cockpit" plus "unexplained disappearance" scenario, for which they're not designed, simply doesn't happen often enough to be worthwhile worrying about.
Short version: flight recorders aren't broken, they don't need "fixing"
Long version: imagine you were to propose a major redesign to your employer's systems to attempt to diagnose unaccountable failures which based on historical data happen 0.00000018% of the time[0], what would be the response?
[0] back of napkin maths based on https://news.ycombinator.com/item?id=36284912