As Germany apportions its 99 MEPs on a national basis a party need only poll 5% to  obtain 5 MEPs, and it will get at least one MEP per % vote.

France is broken up into supre-regional constituencies electing around 10 MEPs each, and so 10% of the vote in a region necessary to get one MEP. This makes it harder for the French Green Party to get seats on the EP.

In addition:

His disregard for conventional European politics of Left and Right has made him more unpopular in France than in Germany. The French Green Party and the French Left in general remain more attached to these distinctions, whereas in the German Green Party, the moderate Realo wing had already won over the hard-line Fundi wing, possible alliances with the Conservatives were no longer taboo, and third way policies under the center-left Schröder government, such as Agenda 2010 and the Hartz I - IV laws, found considerable support. He was also accused of not giving to the French party the percentage of income that all MEPs and other elected members are supposed to give to their party, although the party had officially agreed to exempt him before his first election in France. This, alongside his pro-European attitudes, led him to participate to the 2004 European elections on the German side, where he became the highest male candidate on the list and was elected again.