This is likely because the number of viable candidates today is much larger due to population growth and access to media.
In 1904, getting famous was much harder than now, so someone already known to the voters, even as a loser, could have a better chance than a yet-unknown.
I wonder if negative campaigning also plays a role. Candidates like Hillary Clinton and Al Gore have faltered due to the cumulative effect of years of attacks, while candidates like Obama who appeared out of nowhere were more successful.
Check out 19th century negative campaigns. Modern politicians look like kittens. Pamphlets were published comparing Lincoln to an ape.
Candidates like Clinton falter because they suck. Kicking off your campaign Roosevelt Island and driving to Pennsylvania or wherever in a hotel shuttle van was the kickoff to a weak campaign.
The audience was different. Candidates were selected in party conventions in back room deals, the name recognition that mattered was with party machinery.
