Bernard Girard asks, pertinently, why the Greens are fielding a presidential candidate at all, when that candidate (who will surely be Eva Joly) has no chance of winning? Their intellectual heft, Bernard argues, would be greater if they participated in the debates that will be organized by the Socialists. I think this is correct, and it is surely part of the reason that Cohn-Bendit wanted the Greens to focus on gaining influence rather than running for the presidency.
That said, it's no doubt an indication of the maturity of EELV militants that they preferred Joly to Hulot. The latter has greater name recognition and celebrity, which no doubt accounts for his high poll numbers in the general population, but Green militants were apparently put off by his ties to major corporations, an embarrassment given that one of the Greens' principles is to break with the "productivist" logic of the capitalist economy.
On the other hand, I'm not sure that the best way to articulate the passions that motivate the Green movement are through a political party at all. The Greens have long since ceased to be a "single-issue" party, but the essence of politics is compromise, and the existence of a "green"-labeled party in my view has mainly served as an alibi for those who have been unwilling to make the compromises that governing parties are required to make. Non-governing parties of all stripes are good incubators of unorthodox ideas, but they are also vehicles of protest that serve the interests of those who value ideological purity over compromise. Sometimes this is healthy, sometimes not.