Otherwise, no one would give a rat's ass about mildly attractive, vapid, pathologically lying, party girl Casey Anthony.
But from a broader perspective, the Anthony story now is about the social compact. How do we treat a member of society accused of the horiffic crime of killing her own child, but one found "not guilty" of the crime in a court of law? In theory, we are to treat those found "not guilty" as though they are "innocent," which is not the same thing. "Innocent" means you didn't do it; "not guilty" means simply that the prosecution was not able to convince a jury of the accused's guilt beyond a reasonable doubt. And the story now is about this distinction.
We, as a society, have decided we would rather err on the side of freeing a certain percentage of guilty parties in favor of imprisoning a similar percentage of innocent parties. The burden of proof lies with the state, and "beyond reasonable doubt" is a high hurdle. This is a decision that yields occasionally, apparently, outrageous results: as with OJ, as with Casey Anthony.
So now we have this exotic social outlier, whose notoriety is a potential economic engine, with vast resentment stored in the body politic because she appears to be suffering no consequence regarding the death of her child; and to add insult to societal injury, is in fact living a life of luxury as a DIRECT result of her presumed crime.
That's why we are outraged. That's why we are still interested.