Senor Beef nailed it; the absurd media coverage lends a certain cachet to the idea that if you perpetrate one of these atrocities, you’ll definitely get your 15 minutes of fame, and then some.
I mean, if you look at the lists, the vast majority took place after the introduction of the 24 hour news cycle, and of those, they seem weighted to the post-internet time frame.
You can’t tell me that the Bath School Bombings were more than a small article in the say… Atlanta, Dallas or Kansas City papers, or more than a brief mention on the radio when they happened.
But nowadays, it would be all we heard about for days, and the stories about the killer and glurge about the victims and their families would haunt us for years.
So clearly the phenomenon isn’t caused by news coverage, but news coverage certainly makes it more infamous or “popular” or whatever, and that’s usually what these types are looking for.
Not incidentally, that’s the raison d’etre of terrorism as well.