This is a theory, and I will probably get hosed, and flamed
The best answer I can give you as for why people are using a MAC as an alternative would be that the options available now for solenoids are probably more limited.
As far as I know, only Virtue and Seventh element are making the more conventional solenoid/board set-up. There may be others, but I have not seen them.
From a pricing standpoint I can tell you the alternative is very good as well.
Damon over at scenario dreams sells MAC 33 and his universal T-board for a very reasonable price.
I have pondered running this set-up for awhile now.
Let the flaming begin !!!!!