You make some very good points and I don't entirely side with those who say you're callous or whatever. To answer your question, I think the fascination with this case as opposed to the others you cite has to do with humans' sense of justice or, in this case, justice denied. In this case, she has meaning for us that the others don't yet. We could all imagine it, so it is more real. There has been no closure (apologies for the pop psychobabble), so we are unable to let it go. We, especially those with kids, wait for justice and answers as to who did it and why.
I agree.
I've gone back and forth on whether or not I think Patsy was complicit (author of ransom note). I decided years ago that I couldn't really tell. This new "suspect" may or may not shed any light on the case. If Patsy Ramsey is innocent, I sure would like to see her completely vindicated (and vice versa).
The fascination with this case is easy to explain:
1. It is a case the media chose to turn the white hot light of its interest on.2. The media did so because the family is wealthy, the mom was a former beauty queen, and the victim was a gorgeous 6-year-old girl. Better yet, there were plenty of stills and video of the girl the media could salaciously run over and over and over and over again, the better to boost ratings and ad sales (and, let's be honest; to feed plenty of people's sexual fantasies).
3. The case is one heck of a mystery. A real-life TV murder movie. Most of us love a good mystery.