Silence is habit-forming, isn't it? If your daily routine requires--or at least results in--isolation, and in addition you spend the majority of your free time alone, you lose not just the opportunity, but also the desire to share your thoughts with other people. All communication is inwardly focused, and the external world ceases to exist after awhile. It's a subtle but possibly irreversible slide into reclusivity.
I used to think that becoming a hermit would take work, or that at least I would feel some level of sacrifice, giving up social interaction and stimulation. But it's the exact opposite: becoming and staying alone is easy. The effort comes in remaining connected to the people I (used to) know. It's so simple to postpone speaking, hoarding my thoughts and forgetting--refusing--to share them later. It's easy to be lulled into a state of complacency, reading my own mind and keeping my own counsel. Participating in public discourse takes on the form of self-betrayal, and in the end, it's more rewarding to pull away entirely, and refuse to answer when people stand at the mouth of your cave and demand that you come out and play.