Lot of Pilots (perhaps Middle East Airlines excluded) get a little confused with the F word and the S word = sleepiness and the need to sleep. Fatigue is long term, Sleepiness is i'm banjaxed on this run of flying.
One of the biggest issues for Pilots is that airlines are now using scheduling systems with fatigue models attached to them. They check the roster and if it's below the "limit" whatever that is = the roster is legal. One such system is the Boeing Alertness Model for example. The main issue is these systems don't have data. The system should be set up for the specific airline not Airline X. Crews should be completing diary and wearing motion watches so the data is validated.
A lot more work needs doing we can only hope some good will come out of tragedy