The problem was that France and Belgium had occupied the Ruhr area in 1923 to secure coal as a payment for the war reparations that the Germans had problems meeting. They were not supported by the British in this, and the occupation proved to be a costly mistake. The German industrial and coal workers in the Ruhr area went on a general strike, supported by the German government (which printed money to pay them, which resulted in the massive hyperinflation that Germany during the era is famous for). So France had recent experience with using military force to handle the Germans - it had been a costly mistake, both in money, time and the relations with the rest of the world. It also devastated the German economy to the extent that they were unable to meet their payments fully ever again.

1934 the Belgians withdrew from their alliance with France and the depression had forced the French to cut down their military spending.

The French experience in 1936 was that the Germans would not back down short of full scale war, which they could ill afford, especially if not supported by Belgium and Britain. Britain at the time supported an appeasement policy, so the French had to choices (in their own eyes) of going to total war alone against Germany or let the incident slide. They chose the latter.

Edit: Sources.

Svensk uppslagsbok, Gunnar Carlquist and Josef Carlsson, printed 1957. Band 21, pages 667-668.

Ruhr-ockupationen och den tyska socialdemokratin, Heinrich Ströbel, Tiden issue 15 1923.