We all know how checkmate evolved. Before, you’d capture the king.
Now, if your rook is pinned by a bishop, your rook CANNOT MOVE. It is against the rules of chess.
If your rook cannot move, why can’t your opponent move her king onto the same
unobstructed rank or file as the pinned rook? The rook does not move diagonally and
does not move when pinned by a bishop. The rook ONLY moves along ranks and files
and then only when it is not pinned.
The answer is that if the king moves there, historically you would capture the king before
your opponent would capture yours, and you would win by capturing the king.
Perhaps more historically, if you were a king and one of your men killed the enemy
king, his men would have no commander and would surrender to you, lacking any
other instructions.
So the rule that says a stalemate is a draw, is a logical extension of the rule against
making moves that put your king in check under any circumstances.