Their small size is a result of their evolutionary adaptation to their environment, which includes living in trees and other vegetation where smaller body size and lighter weight provide advantages such as greater maneuverability and ease of flight.
As for their messiness, budgies can be messy eaters and tend to scatter their food and droppings around their cage. This behavior is natural for birds and is a result of their foraging instincts, as they are accustomed to searching for food and water in the wild.
Owners can help to manage messiness by providing their budgies with appropriate feeding dishes and keeping their cage clean. Regularly cleaning the cage and providing fresh food and water can also help to reduce mess and maintain good hygiene for the birds.