I like Rolling Stone's take on this issue. Their basic view is that the "No on 8" was outgunned, plain and simple. The "yes on 8" people had more money, better advertising, and more man-power. Ironically, the "Yes on 8" group were the ones who took the ground game strategy to heart:
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Throughout the summer, Yes on 8 deployed an army of more than 100,000 volunteers to knock on doors in every zip code in the state.
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The Yes on 8 campaign's get-out-the-vote effort was equally prodigious. The weekend before the vote, Schubert's religious volunteers once again went door to door, speaking to supporters and directing them to the right precinct locations. "On Election Day," he says, "we had 100,000 people — five per precinct — checking voter rolls and contacting supporters who hadn't showed up to vote."

So, yes, get better advertising, but also get people out and involved in the campaign early on. (Hey, I read about all the protests. Surely they could have volunteered to help before the vote, if only the campaign organizers had asked.)