Why we can only estimate that 300000 people died as a result of the tsunami?

Question

Why we can only estimate that 300000 people died as a result of the tsunami?

Answer 1

Many bodies were never recovered. Washed out to sea, buried under tons of rubble, etc.  

Answer 2

Bodies lost and lack of accurate figures on population.  If a landslide buries a village in a regulated place, the number of dead can be accurately estimated by counting those alive and subtracting from the census.

  But if population is only loosely known, especially if people migrate in and out of the area to fish, etc., and if people are free to leave the area because it is devastated and their "jobs" can be done down the coast or inland, then there is no good idea of how many were there in the first place and how many just wandered off before counting survivors began.