Confused by XE Trade rates

Hello, Im Canadian but have just moved from Australia to the UK and want to move my money from my Australian to British bank account. I wanted to avoid big bank fees and so went through the lengthy process of signing up with XE Trade.

I spent WEEKS setting up an account with them and finally got it set up today and they quoted me 3268GBP for sending 5000AUD. this works out at around 4% commission (£157). I was surprised by this as the reason I had been spending so long getting set up with XE was because I read on here and a few other places that their rates are really good, like 1.5%.

I was offered-:
XE Trade conversions:
1GBR = 1.5299 AUD
1AUD = 0.6536 GBR

Actual rates:
1GBR = 1.46 AUD
1AUD = 0.69 GBR

In the meantime ive been withdrawing money using my Australian debit card at ATMs to support myself. £300 a go and paying around $450 which means around $16 in transaction fees (around £11). so I could theoretically just withdraw my $5000 in 11 withdrawals and pay £121 instead of £157.

I just dont get it, i feel like Im missing something. Is the reason that its cheaper is because most people arent in the position to just withdraw the money abroad because
a) they arent there and
b) the amounts would be too large?

Thanks for any advice anyone can give.