Sometimes people don't respond because they don't know what to say. Or maybe you said something that makes them feel uncomfortable. (I am not saying you're doing anything wrong, but for example, if you sent suicidal stuff, people may not know what to say and they may feel uncomfortable in responding.) Sometimes people even genuinely forget to reply on occasion. So it really could be a mix of all 3, for example. But like you said, there are a million reasons someone could have for not replying.

I think it is important to focus on yourself and not let your happiness be dictated like other people. For example, don't you ride your bike 100 miles nearly everyday? You could do that to keep yourself busy and distracted. But also, since you are a retired doctor, maybe you may find it interesting to read about modern medicine achievements and advancements. Another thing you could do is go to that used bookstore in Portland and find some books to read. Heck, you can even write blog posts on your experience in a super max facility to help others who are going through similar situations. Surely people want to read about your unique experiences? Basically, turn your negative thoughts and energy on this topic into something positive. Don't worry about what other people think. They aren't good friends, in my opinion, if they are purposely blowing you off. Good friends don't do that.

If your honesty about your illness is what bothers them, then that's on them, not on you. You're being honest by opening up and sharing your true feelings.