You have to ask
Despite what you think, you are not as approachable as you think you are.
“My door is always open” doesn’t work.
You have to notice when they have something to say that they aren’t saying, then you have to invite them into your sanctum, sit them down with a cup of coffee and an encouraging smile … and ask them how things are going. Then give them time to warm up and say what they weren’t saying.
You have to approach them.
You have to put yourself in the places where they are and actually show (not just tell) your interest.
Likewise, despite what they tell you, they are not comfortable giving you feedback and contrary opinions. You have to ask for it, accept it with good grace, smile, thank them and show that you listened.
Skippy strategy: Despite what you think, you have to make the first move.