People will generally go towards whatever activity best satisfies their personal needs/desires. For kids between 13/14 and 17/18, there's a lot of stuff competing for their time and attention. Personal relationships, school (regular and "additional" activities like sports or more classes), work, family, just plain goofing off, there's a lot of stuff going on.
Give kids the ability to plan out their own fun activities (as they define it) and they'll choose Scouting. That doesn't mean toss them a notepad and tell them to plan everything. Sometimes they need help, sometimes they need training. Think of how planning meetings can be improved and go from there. Most of a planning meeting can likely be done via various forms of social media. Sitting around a table while one person talks and occasionally a few people brainstorm while most people remain silent? That's a recipe for boredom and disconnection. Chat about activities via Facebook messenger, texts, Google Drive for documents, that'll get people's attention. Then how to plan an activity? What do they need? Maybe some leading questions need to be asked like, "What are you going to eat?" if they've never planned something like that out, then perhaps they need some sample menus to choose from. Perhaps they need to be pointed at additional resources.