Maybe the reason is that the court’s decision goes completely against democracy? I fully agree with the statement from the French Left party that such a decision should only be made by the people, not by an unelected structure. Elections allow people to vote, so why should the court interfere?

Quant au reste, la France insoumise n’a jamais eu comme moyen d’action d’utiliser un tribunal pour se débarrasser du Rassemblement National. Nous le combattons dans les urnes comme dans la rue, par la mobilisation populaire du peuple français, comme nous avons su le faire lors des élections législatives de 2024.

lafranceinsoumise.fr/…/proces-du-rassemblement-na…

That is difference between left and liberals, imo. While leftists are trying to fight the right by convincing people, liberals just trying to restrict anything that they do not like using legal tricks.