I do think this case was popular for quite a few reasons, here we go:
A. Scott Peterson's extramarital affair - which certainly didn't give the jury any reason to think that Scott Peterson was the boy next door. I think it might have pissed off a few female jurors to know about it. Then again, I can't help but think that he may have killed his wife because he didn't want to live with her, and instead, live his life - or at least part of it - with Amber Frey. Sad thing is, she didn't even know Scott was married.
"First of all, I met him on Nov. 20," she told reporters at the time. "When I was introduced, I was told he was not married. Scott told me he wasn't married. We had a romantic relationship. When I discovered he was involved in the Laci Peterson case, I immediately contacted the Modesto Police Department." - Amber Frey
B. Laci was Pregnant - definately got the pro-lifers' attention. Maybe Scott didn't want to raise a child and Laci did? It probably kept going for speed because of the whole election year, and people want to hear news that isn't always exclusively political.
C. Laci was Very Young - she seemed like a fairly attractive girl next door type, who deserved much better than the card she was dealt. Scott also seemed pretty young, and I heard quite a while ago that some women wrote him love notes while he was in the slammer.
D. The Many Faces of Scott Peterson - He changed his looks, dyed his hair, and grew a goate around the time he was considered a suspect. He also took a suspiciously large amount of money with him.
E. It Happened in California - and California gets a lot of press attention. The average nobody on the street knows who their governor is, and so forth.
F. Mark Geragos - one of the most famous lawyers alive. Backed Michael Jackson for a while, and insisted that Peterson was innocent even after the guilty verdict. After the result of this case, I must say, Johnny Cochran is better at making nonsense comments.
I probably left out some points, but I can't think of anything more at the moment. I'm pretty sure I nailed the core, but if I didn't, feel free to correct me.