HF communication?
I haven't flown in that part of the world for a few years now but is it all VHF comm on that route? Were the crew loaded up with HF position reports etc. In those conditions the weather radar returns can be daunting and it looks as if a huge diversion was in order to "get around" the Cumulo Nimbus build ups. The Captain may have felt that by climbing higher he would have gained visual cues as to a best route through the CBs. The SigWx chart would have left the crew in no doubt that they could not have climbed above (max FL390 for A320) the thunderstorms in that general area. Hopefully the crew were given plenty of fuel on board for the necessary weather diversion. Some airlines have the capability to give weather advisories from their operations department while others do not. It's often times down to the pilots to use the weather radar to the best of their ability to thread their way through.
Detecting CBs on radar in this part of the world (ICTZ) is not as straight forward as in higher latitudes in my experience.
If this doesn't end well my sincerest condolences and sympathy to all concerned.