Ants enter your home for a variety of reasons, but most commonly to find food. Ants, like humans, must feed to survive. Their young must be fed. They don't mean to bother or distress you. They are just like any other animal, insect, bug, or plant on Earth attempting to survive. Your house could be a food and water source. It can also protect nascent colonies from predators and the elements, allowing them to expand when they're ready. Obviously, you'll want to stop this infestation and colonization whenever possible.