15-25 years ago, was pretty friendly with the lady who ran one of our local dairy farm stores, her husband ran the farm itself. They did and still use those glass returnable bottles, and I remember her mentioning the state or the CDC were making it increasingly difficult for them to continue operations as they always had, requiring the purchase of new equipment and implementation of new processes that made it almost impossible to remain profitable. I got the sense that if they weren't already well-established and already approaching retirement, that they'd have never been able to afford to be in the business of direct retail.
Most of our local dairy farms sell to one of a half dozen larger dairy conglomerations, who combine and process their milk for modern packaging to stores.