I would think the cost to haul them back would be pretty low, as the distributor's truck has to go back to the bottling plant anyway.
I would also think that the cost of cleaning them would be less than the cost of melting sand to make new bottles.
melting sand is very cheap
No, because the truck rarely goes back to a plant. It generally goes to a warehouse where the bottles would have to be unloaded and then reloaded into another truck which would take it back to the plant. These trucks are rarely deadheading, they generally haul other things on the return trip.
They would have to assign part of their plant for bottle cleaning, buy special equipment to clean the bottles, use special chemicals to clean, buy more special equipment to inspect the bottles, higher liability insurance and so on. Since they buy the bottles rather then make them it is cheaper to buy them.
I know of a local dairy company that is using glass bottles for milk. Since they have a small specialize clientele reusing works for them. On a large scale it would add to your costs.