Here's why:
* "Émotion" is the French word for emotion, and it ends in "-ion". Nouns ending in "-ion" are typically neuter.
* Gender agreement in French applies to adjectives and articles, not nouns themselves. So, you would say "une grande émotion" (a great emotion) or "un sentiment profond" (a deep feeling), using the appropriate feminine or masculine article depending on the adjective.
Therefore, emotion itself is not gendered in French.