Zach and Nicolette likely chose a dog as their pet due to the companionship and loyalty that dogs provide. Dogs are known for their playful nature and ability to bond closely with their owners, making them ideal for families or couples. Additionally, having a dog can encourage outdoor activities and social interactions, enhancing their relationship and lifestyle. The responsibilities of dog ownership, such as walking, training, and caring, can also strengthen their partnership as they work together to ensure their pet's well-being.