Ask Cast Members who buys the reusable bags and if people buy all 3 sizes, you will find the answer is a huge percentage of customers buy all 3 and don't use them.
Your view on this is absolutely correct. It makes no sense if your goal is to cut down on pollution but if you think Disney's goal is to sell bags and make money then it makes perfect sense. My wife has been collecting plastic bags this the reusable bag policy was announced and now she is collecting the reusable bags. Look at Ebay and see all the bags, plastic and reusable, for sale.
I usually decline to purchase at all with the poor quality merchandise and the ridiculous prices.
So no issues with bags for me.
I did sometimes grab a “to go” bag (the inkless kind) from the food court to carry in my Vera Bradley purse and put to use as a “purse raincoat” in the event of a downpour. It often came in handy. Better than the ones from the shops that would get blue all over you.
I made a point to put them in the recycle bin in the hotel room.
Now the main purchase they get out of me is the Pandora charm I can afford using my no mousekeeping gift card!! Again, no bag needed.