To figure out why you can't have a guinea pig, you'll need to ask the people who are saying you can't. It could be for a number of reasons:
* Age: Are you too young to take care of a pet?
* Allergies: Do you or someone in your family have allergies to guinea pigs?
* Space: Do you have enough space for a guinea pig cage and its daily exercise?
* Time: Do you have enough time to care for a guinea pig, which needs daily attention?
* Financial: Do you have enough money to provide for a guinea pig's food, bedding, vet care, and toys?
* Responsibility: Are your parents or guardians concerned about your ability to be responsible for a pet?
Once you know the reason, you can discuss it with your parents or guardians and try to address their concerns. Maybe you can work out a plan to show that you're ready to care for a guinea pig!