Why are the walls not listening to George on his command?

In Ray Bradbury's short story "The Veldt," George and Lydia Hadley purchase a "Happylife Home," which is a technological wonder of a house that does everything from cook meals to draw baths and read to its inhabitants. George spends extra on a nursery for his children, ironically named Peter and Wendy—the same names as the children in the classic tale Peter Pan. The nursery responds to thoughts and has crystalline walls that cause 3-D representations of whatever the inhabitants think about to appear. It doesn't just have pixel-sharp images; it also has sounds and smells.
The story opens as Lydia expresses her concern that something is wrong with the nursery. She asks George to take a look. He encounters an African veldt with lions eating something unidentifiable in the distance. Lydia wants George to lock the room for a while, but George is hesitant because the children are nearly addicted to it. When he goes back into the room later, he tries to get the nursery to change scenes, but it does not:

He knew the principle of the room exactly. You sent out your thoughts. Whatever you thought would appear. "Let’s have Aladdin and his lamp," he snapped. The veldtland remained; the lions remained.

When he tells Lydia about this, she suggests that the room can't change because the children have thought about Africa so much that the room has gotten in a rut. It's clear that this room is the children's space and that the parents don't monitor it often. It seems logical that the parents can't change the scene in the nursery because the room has adapted to the majority of the thoughts being about Africa and can't change. Later in the story, chillingly, readers find out that it is a plot the children make to get rid of their parents.

Since the environments are connected to the children's thoughts and George doesn't use the nursery as much as the children, it can be assumed that he didn't have enough experience to control the setting of the nursery with his thoughts. Prior to checking, George and Lydia comment on how the children used to create fantasy landscapes. This suggests that the nursery mainly responds to the thoughts of the children.
This also symbolizes a change in power dynamic from George to Peter. Although George is the original patriarch of the family, Peter convinces George to keep the nursery on for a little while. Peter uses this opportunity to usurp his father by locking both his parents inside the nursery as the lions devour them. With both his parents dead and complete control of the home, Peter becomes the man of the house.