When the dealer's hand is 17 or more, the chances of going bust are higher, so they stand to avoid taking unnecessary risks. This strategy is based on probabilities and aims to maximize the dealer's chances of winning while still providing an enjoyable and fair game for the players.
When holding nine or less or 12-16 it's best to hit, but stand on a total of 17 or more. If the dealer's card is a four, five or six it is vital you do not bust. It is common practice to hit on eight or less, but stand on anything 12 or higher.