bluegreen said:
some suggestions are:
timing – planted late in the season not allowing enough time for bulb development before the days started getting longer triggering flowering
overcrowding – not enough room for bulb development
too much nitrogen – grows lush tops at expense of root development (although this does not sound like your problem)
stress – a sudden onset of heat or the soil drying out causing stress to trigger flowering
you could add pH (needs slightly acid 6.5), not enough or too much sun (i’m not sure of sydney but they grow in full sun during winter here in adelaide), lack of drainage, lack of thinning.
BG’s first one – planted too late in winter – is the most likely