Mostly because the clowns that make those 3rd party maps, units, etc. are total clowns.
All they do is help destabilize the game with their amateur skills. Wow, sick and tired of such retards making 3rd party mods who don't know what they're doing except making good games unstable.
They can go to heck in handbasket.

Just stick to the original GOG-treated game if you want to save yourself a headache.

They are extremely unstable when trying to add to the Mac GOG package. I have had a lot of success building my TA with all the maps units etc in Windows (VM through parallels) and then copying them over to the Mac side. After that I use Wine Bottler to package and its been working perfectly since.

Personally I incorporated the 3.9XXX Community patch plus The Pack mod which adds a lot of units and improves the AI a bit.