We're a small team of around 15-20 people. Around 70% of them are really passionate in what they're doing, visit conferences, spend even their weekends on hackathons and have a big progress in their skills. It's really fun to spend time with them and seeing how they evolve, which again also pushes me to keep up to date.
But there are also some guys (the other 30%) who don't have that will to go outside and even when we tell them how great an event was, they don't want to visit them. The company is paying hotel, transfer and so on, and there are also also events on weekdays, so they don't even have to spend their free time. No chance, we trief it several times and don't know how we can motivate them. These guys are currently doing great jobs, but there might be problems in the future when all other still get better and better and they loose the connection to the group. Also personally I think even, if you're already great you can always get better and it's also a great feeling to show other people what you're doing and exchange your knowledge.
When we ask them why they don't wish to attend, their response is that they are "just not interested."
So what can we do to encourage these people? We don't want to force them, I don't think that will lead to something efficient, they have to be willing themselves to visit events and improve their skills.
Edit: Thanks all for your great answers and you're right, we need to ask them more directly and work together to improve their skills, even on their own ways.