Is this a shock to you? Plenty of people do. This is going to be particularly true for the Canada Line folks, who may not have any Canadian currency on hand.
People who have a card or tickets wouldn't be using the machines in the first place, so they are not the type of people Translink needs to focus on when they decided what type of ticketing machines should be used.
And who are these normal people who carry buckets of change?
I'm not a frequent enough transit user to warrant the need to buy a monthly pass, and I don't think the savings are enough to pay a good chunk of money upfront for those books of tickets, as it would take me forever to use them up. When I take transit (about once a week), I use it a lot that day so I buy an all-day pass. I don't think using my card to pay for a 9 dollar item is particular crazy. I even use my card to pay the two bucks for parking at Scott Road Station!