For the same reason that children adopt virtually anything.
Within the context of their general development, children are undergoing a long process of constructing their social architecture.
Which often entails a long stint of unsophisticated and ruthless social climbing. Therefore, anything that is presented to them as being socially advantageous stands a chance of being adopted.
It isn't much different in nature from blue-blood adults consciously adopting the Mid Atlantic Accent.
Within the context of their general development, children are undergoing a long process of constructing their social architecture.
Which often entails a long stint of unsophisticated and ruthless social climbing. Therefore, anything that is presented to them as being socially advantageous stands a chance of being adopted.
It isn't much different in nature from blue-blood adults consciously adopting the Mid Atlantic Accent.