Why Is It So Hard For Canadians & USians To Get CA Halves.

It is difficult for me to understand why halves don't circulate.
Australia has half dollars (50 cent coins) which are even slightly heavier than the U.S. halves,
and they are in common, normal circulation.

Could it be the result of the spread the face values for the circulation denominations?
Australia has:
1 cent coins (no longer issued, negligible buying power)
2 cent coins (2x), (no longer issued, negligible buying power)
5 cent coins (approx. 2x)
10 cent coins (2x)
20 cent coins (2x)
50 cent coins (approx. 2x)
1 dollar coins (2x)
2 dollar coins (2x)
5 dollar notes (approx. 2x)
10 dollar notes (2x)
20 dollar notes (2x)
50 dollar notes (approx. 2x)
100 dollar notes (2x)

The only thing illogical about this system is that one dollar coin is larger and heavier than the two dollar coin.
The 5 cent to 100 dollar denominatioins are ALL in COMMON circulation.

I was in the 'States a couple of years ago, and found pennies still in circulation. I found them very annoying.
It seems that they are made for single transactions only, and are then hoarded, to be handed back to the banks in bulk.
The banks would find that situation very annoying, as well!