People may have a preference for a particular gender of dog for a variety of reasons. In the years that I have been breeding, I have observed a phenomenon that I want to call a phobia. A fear of a certain gender, based on the unknown interactions with a particular gender of dog and how the bonding would be affected. It is very real, and it is also very strong.
When a person develops the opinion, almost always as a result of never having a certain gender of dog in their lives, they are strongly opposed to trying to bond with a new puppy of that gender. It is usually males based on stories of marking or humping. But it can be a fear of grass staining from female urine or never having a female dog. All of those fears are easily remedied, but the fear of it keeps buyers very firm in their opinions.
Here are a few other common reasons why someone may prefer a male or female dog:
Temperament: Some people believe that male dogs are more aggressive and dominant, while female dogs are more affectionate and easier to train. However, this is not always the case and can vary based on the individual dog's personality, breed, and how they are raised.
Size: Depending on the breed, males may be larger and wider than females. This can be a consideration for people who prefer larger or smaller dogs.
Compatibility with other pets: If you have other pets in the home, some families prefer a male or female dog based on their compatibility. For example, if you have a girl dog already, you may choose a male dog. Often people like to balance out gender, even with animals.
It's important to remember that while there may be some general differences between male and female dogs, every individual dog is unique and their personality and behavior will be shaped by a combination of their breed and how the breeder raises them.