My guesses as to why this dead kid show did better than the other dead kid show:
1) This sort of show plays better on a Sunday night than a Thursday night.
2a) People actually pay attention to ABC, as opposed to Fox, so viewers were aware S&L existed.
2b) ABC's audience is more likely to like this sort of show than Fox's audience.
3) S&L doesn't have anyone faking a bad American accent.
4) On the subject of David Tennant, the audience may find Ryan Phillippe to be the more attractive of the male leads.
Yeah, but American Crime was the best show of the three! (And I get why American Crime isn't doing well. Which sucks. It's too raw).