• In 2002, the far-left was not united: there were as many candidates of the far-left and, together, they made 19,06% of the votes (and you can add 5,33% for Chevènement). So the lack of unity doesn't explain the poor performance.
  
• This remarkable performance was achieved by attracting voters who would have voted for Jospin (he obtained only 16,18% of the votes)
  
• Abstention was much higher

And he doesn't explain why the far-left can't unite!

"Dieu se rit des hommes qui se plaignent des conséquences alors qu'ils en chérissent les causes" Jacques-Bénigne Bossuet