1. The storm did not look bad enough to deviate around.
2. The line of storms was so long and uniform, it would not seem to matter where they penetrated.
3. The pilots did not have enough training in Wx radar ops.
. a. Nobody was looking at the radar returns.
I believe 1., 2. are more likely than 3. or 3a. The whole WX deviation thing may be a red herring. In the animation that PJ2 posted, we can see the ELY flight flying without any deviations. In fact, it looks like it flew through a cell comparable to the one AF447 is projected to have flown into.
I think AF447 was unlucky to have entered a UAS condition. (quite independent of weather conditions.) AF knew this was always a possibility, no matter how remote. Hence, the pitot replacement program.
Two other possibilities I'd like to add to the above list, if I may:
4. Crew noticed something anomalous with airspeed and were fixated on understanding the situation.
5. Crew noted the weather ahead but deemed it a lower priority issue than something else. (If so, what is the USD 64K question)
But the pilots would know that NORMAL LAW is u/a, so why try to latch a/p only to see it booted (rejected) by the computer again??
Could this be the last actions of a crew desperate to get out of it...