King Dedede lives in a castle because castles are traditionally associated with royalty and kings. Castles are large, fortified structures that provide security and serve as a symbol of power and authority. As a king, it is fitting for King Dedede to reside in a castle, which offers the necessary space and grandeur befitting his royal status. Additionally, castles often have multiple rooms and areas, allowing King Dedede to conduct his royal duties, host events, and entertain guests.