When the new Vertical Ten came out one BMO branch refused to order some bundles for me. She told me they had too many of the commemorative and old Tens to warrant an order. So, not entirely sure why, but they're just not as popular a denomination.
I wouldn't say they're refusing to order some bundles of the new vertical tens for you. They're likely refusing to order tens, period. Considering that the banks have been going through the existing supply of tens slower than a snail's pace, it wouldn't shock me if the branches are considering that supply as their official last order of tens, and once they are gone, the branches (including the one you're referring to) will not be ordering tens anymore.
There was a time back in the day when $100 and $50 bills were hard to come by the same way the $10 bill is hard to come by nowadays. I wouldn't be surprised if the number of tens in circulation now is basically the same as the number of $100 and $50 bills back in the 70s but no later than the 80s. And the ten has spent most of its life cycle in decline, it seems. It is basically a redundant denomination because $10 is exactly double of a $5 bill, and the $20 is exactly double of a $10. The more divisible denomination is more important in our currency, but not the ten.
I got one question: If the Bank of Canada were to retire the $10 bill some years down the road, I bet the number of $5 bills will (more than) double if purchasing power of the $5 becomes $10, and in this case, do you think the Bank of Canada will consider a $5 coin by that point?