Churchill's explanation was that the public sentiment in the Allied countries, and in particular in France, made it impossible for the Allied politicians and diplomats to do anything other than cut out pounds of flesh. A generation had been cut down in its prime, and the public weren't interested in nuance, only in punishment.

Imho The French wanted payback for the war and humiliation of 1870/1871 and the Brits wanted to make sure they were not being contested by a country with the potential to become more powerful than they were especially since the empire was crumbling.

In a nutshell because the french wanted revenge for the franco prussian war