I had my amex card cancelled because i topped it into credit and asked for a refund, didnt know it was a no no in the credit card worldIt's a premium, top-level credit card you're paying for the privilege of holding. It would be beyond bizarre for it to be cancelled with no notice and no explanation unless something has gone on with its use you're not revealing for whatever reason. It's equally suspicious that you're not very much more upset about it and just looking for possible answers in their T&C's to find an explanation. It sounds like you were half expecting this situation because you know how you've been using it.
I think your experience is unique to you only and does not reflect more widely on the rest of us with similar cards who have perhaps not gamed their system to quite the same extreme as you have. Just surmising with no evidence, but maybe they ran an audit that highlighted the customers who were the least profitable to them. ie. those who were maximising the benefits to an extreme, while at the same time carefully avoiding all costs and charges, and have simply decided to 'off-board' them with extreme prejudice.
Filed a afca claim, got told afca cant do anything, and in their experience, they use the "commerically unviable" reason all the time