The problem with many simple churches is that they are too good at what they do. They become so “tight” and committed to one another that they become stagnant. That isn’t intentional, of course, it’s an accident. Good friends just become delighted with one another. But that means that there’s no room in the group for others and that’s a problem that won’t go away by accident, either.
Groups need to be intentional about being “Open To New Friends.” Maybe every group needs to designate someone, or a couple, who is OTNF. If it can’t be the natural response of the group as a whole, maybe everyone should agree to at least make it intentional and be on the lookout for folks that need to be received and are looking for a place to “belong.” Seems to me that churches of all kinds need to be ready for new friends.