It just seems illogical to me. France had a bunch of reasons to declare war on Germany in 1936: the hostile irredentist nature of Nazi Germany that threatned the French rule over Alsace-Lorraine, the refusal to continue paying the reparations imposed by the Treaty of Versailles and, most importantly, the remilitarization of the Rhineland. Not to mention that the german army was extremely unprepared to go to war in 1936. Maybe it is because of hindsight, but France (and Britain) just seem to have outright ignored Nazi Germany until the very last straw that was the invasion of Poland in 1939.