Wait . . . The heck? They can produce that Big Zam so much????
the zabi probably ordered a bunch of them to be manufactured but due to the time constraints (or the timeframe of the one year war), they only have the manufacturing capabilities to only make one that is fully functional and battle ready by the end of that war.
after that, zeon remnants/zabi loyalists probably continue with the manufacturing (before moving to other big boys like neo zeong or refining psycommu technology) in hopes they could raise another uprising. then again, zeon's engineering and ingenuity is remarkable despite they have limited access to materials and lower/smaller manufacturing capabilities when compared to EFF.