Unfortunately there are two concepts in Limesurvey:
1. Answer options, they do not have relevance equations (for example the items of a dropdown list)
2. Sub questions, they do have subquestion relevance (e.g. Array questions, multiple choice, etc.)
You are not the only one that is missing answer option relevance.
I answer at the LimeSurvey forum in my spare time, I'm not a LimeSurvey GmbH employee.
No support via private message.