Winterymix - convection intensity over the open ocean doesn't vary much day/night since sea surface temperatures have very little diurnal variation. However convection over the land not far from the LKP would decrease overnight leaving more 'airspace' over the adjacent sea for CBs to develop and peak towards dawn (without going into the broader scale MET dynamics).
This paper:
Analysis of overshooting top detections by Meteosat Second Generation: a 5-year dataset - Proud - 2014 - Quarterly Journal of the Royal Meteorological Society - Wiley Online Library shows that, at least in Tropical waters off Africa, convection peaks at around 08 or 09 local time. In the ocean far from land it's around midnight and over land it's in the evening. The same is, at least on the day of the accident, true for the region around Indonesia/Singapore. Because there's so much land over there the sea is never truly isolated so we get the 'coastal' convection system with peak intensity around daybreak.
Nice clarification about convective threats in the environment of interest. So...what did the other several flights in the area at the time of interest know or did they simply get lucky?
I think a better question (assuming that weather was a factor) would be: What made this particular flight unlucky?