Why do a King only moves 1 step at a time in Chess?

Answer 1

Why not? :)

The king is actually a decent fighter when there are no enemy rooks or queens to worry about. It doesn't have the range of a bishop, but it's not restricted to its own color. It can't jump over other pieces or move as quickly as a knight, but its movement is more straightforward and doesn't have potential moves cut off by being near the edge of the board as easily. Its movement also tends to be helpful in getting a pawn to queen, whereas maintaining control over a pawn using a single bishop or knight is impossible. If a game comes to down to a king and pawn versus king, then, depending on the board position, that king may allow the pawn to queen.

Also, if the king were more powerful, it would be more difficult to checkmate it. For example, if a king moved like a rook or a queen, it would no longer be possible for a white rook to deliver checkmate to the black king without help from another white piece (since the black king could just capture it). This would probably mean that games would be more likely to end in a draw.