Why OFDM is more appropriate with MIMO than other multiple access method?
One possible answer is given at the beginning of the text:


  Raleigh suggested and later proved that the processing required by
  MIMO at higher speeds would be most manageable using OFDM modulation,
  because OFDM converts a high-speed data channel into a number of
  parallel lower-speed channels.


Also:


  MIMO-OFDM is a particularly powerful combination because MIMO does not
  attempt to mitigate multipath propagation and OFDM avoids the need for
  signal equalization.