I have two "conspiracy" theories on this:
#1: EA is launching their own digital distribution store soon. Maybe they are keeping the complete version for their own platform.
#2: As many of you are aware, prior to this re-release on GOG, the only source of SMAC was from Sold-Out software (which can be had via Amazon). I wonder if EA signed some sort of "exclusive" distribution agreement with sold-out and the only way to get around that was to only allow GOG to sell SMAC without SMAX.
I guess I am a bit skeptical of theory #2 though since GOG does not seem to be releasing expansion packs for any EA games, even though not all of them are sold through Sold-Out.
So perhaps greedy, greedy, evil, evil EA is holding out the complete version for their hopefully terrible Origin platform?
Any other theories?