Suggesting tag synonyms requires 2500 reputation which seems REALLY steep for something so basic. It's strange because there is a badge for 3 such suggestions yet it's only considered a bronze badge.
2500 may seem high now, but 2 or 3 years from now, I assure you -- it won't.
The limit is there to ensure that truly experienced users are coordinating on the tags, which are the primary organizational system on the site.
It's OK if only a few users and the moderators are making these decisions now; as the site grows, more people will gain the privilege and can contribute to the process.