Why wasn't the operation of the stick shaker affected by the data entry error? Or was it? (ie, it kicked in later than it would otherwise have.)
The stick shaker and stall warning systems in most commercial aircraft calculate how close the aircraft is to a stall by using angle of attack (AOA) data. It doesn't take into account aircraft weight as the aircraft will stall at exactly the same angle irrespective.
By setting a weight in the computer less than the the actual the crew would have been given Vap and VRef speeds (Approach and landing speeds) that where below those required to maintain an AOA less than the stall (or at least close enough to set off the stick shaker which occurs prior to a stall).
Given the importance of all-up weight, why does it continue to be estimated?
In most cases an estimated weight will be within 1/2 tonne the actual (assuming they operate in a similar fashion to other parts of QLink), and for practicalities sake would have minimal difference on an aircraft of that size.