Re: MIMO-OFDM
This is very good question! OFDM is a very efficient broadband technology. It increases data capacity and the number of users in multiple access scheme, comparing to other broadband technologies using the same bandwidth. MIMO also increases the capacity, and multiple access ability. These two combined together form a Modulation scheme which is very efficient in terms of bandwidth efficiency and throughput.
But I sense there must be other reasons as well that I am not aware of. I would let you know if I find anything else.