The government was deeply divided and on the lead-up to a general election. Neither side wanted to advocate intervention in cae it lost them votes.
French generals overestimated the size of the German army and did not want to risk a skirmish.
They felt unable to act without the British.
Their ideologies aligned well, particular;y their commitments to crushing communism.
It was a useful ‘testing ground’ for new military weapons, and for Hitler to use the Luftwaffe in action.
It provided an opportunity for new alliances: Hitler saw Italy as a more natural ally than Britain or France, and Mussolini was tempted by the possibility of fascist expansionism supported by Hitler.