Answer:
Simple: They didn't want a repeat of the great war, and they also needed time to build up their military.
Step-by-step explanation:
To put it short and sweet pretty much no one in the English, or French, government thought any war like the great war would be worth it, so they went for a policy of appeasment in hopes that possibly the germans would get what they wanted and stop, this, however, was foolish, and hitler/nazis just kept on asking for more. However, this was also a time deal for the french and English too slowly up their military spending and train more recruits however if we look at the Italians and the germans they were annexing swaths of territory and had been militarizing a lot more meaning they spent their time a lot more effectively the French military was also severly outdated and most of the soldiers and people still didn't want war when it started, making it far easier for the Germans to crush them.
The only country that was perfectly ok with another ww1 style of war was the Soviet Union (More so Stalin than anyone) who offered several alliances and chances to crush the Germans before they could get too powerful. The Allies also had a temporary alliance with Italy at the very beginning if Germany attempted to annex or attack austria the allies would intervene alongside Italy. However after Italy invaded Ethiopia this soured relations severly and the allies ended up pushing Italy towards Germany.