Philip, they are telling us the obvious. Typically, aircraft can go through the centreline if: a) too fast a speed for the autopilot to capture; b) a poor (too large an intercept heading) assigned by ATC or a combination of a and b; or c) a disruption of the localiser signal, caused by an aircraft taking off and flying through the beam as an aircraft is about to join the localiser. This can cause problems with the autoflight system, resulting in an overshoot.
I'm sure there are more reasons. These are a few that I've encountered in over 20 years of operating into Sydney.
Hope this helps.
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