Why are there 2 diffrent gauges of railway track in australia.?

We learned all about this when I went to school but I'll quote a website to be certain of my facts.

History of Rail in Australia.

Australia’s first rail systems were mostly built when the country consisted of sparsely settled colonies, before they combined to form a Federation of States in 1901.

By Federation in 1901, all States except Western Australia were ‘linked’ by rail and more than 20,000 km of track had been laid.

Sadly, those who envisaged a nation had not contemplated a national rail network. Three different gauges had been used.

New South Wales adopted the European standard gauge of 1435 mm, Victoria and South Australia built with the broad Irish gauge of 1600 mm, and Tasmania, Queensland, Western Australia and parts of South Australia used the narrow 1067 mm gauge.

For many years, the different gauges handicapped the effective operation of interstate rail services.

The process standardising Australia’s interstate track to a standard, 1435 mm gauge commenced in the 1930s, and was only completed in 1995.

The 3 gauges used were -

New South Wales 4 ft 8½ in (1435mm) gauge

Tasmania 3 ft 6 in (1067mm) gauge

Western Australia 3 ft 6 in (1067mm) gauge

South Australia 5 ft 3 in (1600mm) and 3 ft 6 in (1067mm) gauge

Victoria 5 ft 3 in (1600mm) gauge

Queensland 3 ft 6 in (1067mm) gauge

There are actually three gauges of railway track used in Australia. They are narrow, standard and wide gauges. These three systems came about because the railway networks were developed when Australia was six British colonies each with their own independent government. Each colony operated much like an independent country. Crossing the colonial borders meant customs and excise checks too. It took many years after federation for a single gauge to cross the continent from one end to the other. Prior to that it meant changing trains at Adelaide or Melbourne.

There are, in fact, at least four gauges of railway track. There is the Broad gauge 5' 3" found in SA and Vic; Standard gauge 4' 8 1/2" found in NSW and on the interstate lines; Narrow gauge 3' 6" found in Queensland Tas and WA; and the sugar train gauge of 2ft found up the Queensland coast.

At one stage catching a train from Sydney to Melbourne meant changing trains at Albury from the NSW standard gauge to the Vic broad gauge. To accommodate this, the platform at Albury station was long enough for both trains. The gauge changed halfway down the platform and passengers would get off one train and walk down the platform to board the other. I remember a friend who went by train to Albury and the train stopped at the long platform. After walking the long distance to the platform exit he remarked "Next time do you think we could buy a ticket to Albury instead of the outskirts."

I don't know why, but I do know that at one time, until fairly recently, if you travelled from Melbourne to Sydney by train, you had to change at Albury, because the track was a different gauge for the rest of the journey.