Lol.
Yes that's because if you import the triggers from the 2 files that contain all trigger and variable data they replace the trigger data that you have in your map. Well, it's how WE is made, you have to either copy your other triggers after you import the triggers or add the triggers folder by folder/trigger by trigger instead of importing.
Same with object data, right? You can't expect the import the entire unit data or all object data .w3o and when you import it not to replace all.