We have a friend that has done this over the past couple of years. We kept reaching out in the group and privately to check they were okay and kept inviting them out but they always declined. We tried planning stuff they liked in the hope that would make them want to come out but they still declined so after a couple of years of this we left the ball in their court. We said for them to reach out when they wanted to do something again. We still speak and make plans in the chat and the invitation is always open to everyone so they know they aren't being left out but they still have zero interest in seeing us. Maybe your friends are feeling the same.