Everyone has to pitch in and carry their own weight.Quite frankly, some folks prefer to work alone rather than in a team environment. They’re introverted, shy, nervous, or have bad anxiety.
It is important to bring these people out of their shells. Oftentimes the quietest person in the room is the most reflective and does the most in-depth thinking.
Have the entire team encourage shy people to engage in the topics of discussion. Don’t demand it, but make them realize that you really want to hear their ideas.