Here's why:
* Antonyms are words with opposite meanings. "Indifferent" doesn't inherently imply a relationship with antonyms or synonyms.
* Synonyms are words with the same or very similar meanings. Again, "indifferent" doesn't inherently imply a relationship with antonyms or synonyms.
"Indifferent" simply means lacking interest or concern. It doesn't imply a connection to the concepts of antonyms or synonyms.