What keeps most countries relatively free from terrorism is that they aren't occupying other peoples land or bombing their women and children all the way to hell.
Ever wonder why extremists haven't bombed the Cook Islands or Peru?
Not really relevant to this discussion.
It's nice to be a country like the Cook Islands. You're surrounded by a vast ocean that makes it very difficult to attack. Your interests are also protected other, larger nations, so you don't have to do any "dirty work" to protect them.
You also don't have to spend tons of money on a military and can rely on treaties with other countries to provide your defense.
South Africa meets your definition of a targetable country. Why isn't it attacked by terrorists?
1) The US is a target.
2) The reason it's a target is not what I'm debating.
3) Terrorists are not having trouble attacking the US because they are dumb, as the author stated.
4) Terrorists are experimenting with different ways to attack the US and are evolving.
5) The author of the article is mistaking these experiments with stupidity.
6) The ocean is an obstacle that won't protect the US forever.