Etihad flight to Australia

Caz3121

what is important is what the position was at the time you decided to cancel. If the flights had not been cancelled by the airline then the options were a refund as per the original fare rules of the tickets (unless very expensive refundable tickets then this may have been a small % of the costs) or to accept whatever enhanced waivers that the airline was offering at that time.
If the flight operated (or was still expected to operate at the time of cancellation) then S75 fails.
Many insurance policies will cover restrictions in entry, FCDO advice against travel but will generally be closer to time of departure, eg 28 days before travel. I doubt anybody would have known for certain what restrictions would have been in place for November back in the summer. 
I think your decision to cancel the tickets was made far too early. You could have decided that you were not going to travel and then sat tight and waited to see how things panned out. If flights were subsequently cancelled, refunds would have been possible, if flights still operated and insurance policy covered FCDO advice / country restrictions within 28 days etc you could have claimed. If neither applied then you would still have been able to get the credit / vouchers.