Bidirectional SPI switch?

I can't make it happen. Have a look at the attachment for the results.

-- The idea is that choose either A or B is exclusively
-- connected to C
library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
entity bidir_SPI_switch is
    port(
        A_SCLK, B_SCLK, C_SCLK        :    INOUT STD_LOGIC;
        en, S    : IN BIT
    );
            
end bidir_SPI_switch;
architecture behaviour of bidir_SPI_switch is
begin
    process(en,S)
    begin
-- MASTER enable
        if en = '0' then
            A_SCLK <= C_SCLK;
            B_SCLK <= 'Z';
            C_SCLK <= A_SCLK;
        else
-- SELECT either A or B
            A_SCLK <= 'Z';
            C_SCLK <= B_SCLK;
            B_SCLK <= C_SCLK;
        end if;
    end process;
end architecture behaviour;