It could be many things and it's unlikely that the 5+ out of 10 have the same reason for not speaking. With such a small team you can get to know their personalities and how they behave outside the meeting. This will help guide you to a solution.
- Lack of Motivation / Team Spirit - There could be a lack of team spirit or maybe your team isn't motivated.
If the lack of motivation is macro (the team is affected all the time, not just during this meeting), it will also be the hardest to solve. Causes can be wide ranging, but consider adding side projects, reward systems and acknowledgements.
If the lack of motivation is micro (only related to this meeting) you may need to 'shock the system' by scrapping your meeting. Don't just reschedule the same recurring meeting in Outlook. Cancel it. Create a new one. Change the day, call it something else and change how you run it. Oh, and keep it short.
- Intimidation/Inadequacy - If you have team members that are loud/aggressive/opinionated (not even in a negative way) others may not speak up.
Create a process where everybody gets a turn. Go Round-Robin or Alphabetical or simply call out names.
You can also pre-meet with a smaller group before meeting with the full group. You can then "contribute on their behalf" by referencing back to the smaller group meeting. "I talked with Bob earlier and...".
- Shyness - If outside of this meeting these team members do not talk casually with the group they may simply be shy.
Before the meeting, give a specific task to a specific member. This will give them something specific to contribute and make them the 'expert' for answering questions. This works good when you already know the answer because you can guide them as they answer questions. For example:
"We need some options for logging exceptions. Take 30-min and look into X, Y and Z and see if you think they'd work. See how much they cost and if we can log errors to a central location.".
Then, during the meeting you can ask them direct questions:
"Do any of those allow central logging? Are any of them expensive?"