In order to stop this practice, they would have to execute extra-judiciously some of these truckers and burn their trucks in plain sight for all to see that if they continue this practice there next. They were given a warning about the executions. Since we all know the Trujillismos of the past are long dead for the most part, sand will continue to be hauled away.
It'll stop for a time and then just as the tide, it will come right back. Burning the goods and executing the perpetrators are savageries of the past but they were darn effective at least within the DR. The crooks know the law don't mean business so it'll be the usual cat and mouse game. It will continue until they permanently destroy the environment.