Reusable bags have a number of downsides.  First you have to get them back to the vehicle after you take your groceries in the house, then you have to carry them around the store while you shop and you have to remember to take them into the store too.  How many do you need on a given day?  Take 5, 8, 10, or just 3?  

And as milk often is on the outside of the container from shipping accidents that then is transferred to the bag, making a smelly bacterial laden bag.  Meaning you have to wash it and you wouldn't want to put vegetables in the same bag if it wasn't washed.

I suspect a number of less organized people are going to be sick from using cloth bags full of bacteria because they won't or don't know to wash them.