While they talked about a sandbox style of gaming, they seemed to really mean a player driven method of playing in a closed system.
For years I tried to get gamers playing in my world to go sandbox. They refused to go off script. Even when young characters would stumble on mature dragons they would attack. I suspect it was because several of them were WoW players. In video games every monster was beatable, just like DnD 4.0, all monsters had comparable stats to the heroes. They had the mistaken belief that characters could not be killed, since they were the reason for the story. Even after a few deaths, they continued to try to do the impossible. Even when I tried to explain the concept of sandbox they continued to look to me for the direction the tracks went. When I had given them dozens of hooks they tended to think I was giving them directions.
Not only do many GM's have a problem with sandbox play, but so too do players have a problem with this.