I think if we are to be honest, Britain and France didn't want to get its hands dirty.
Don't forget that Hitler had insane luck to the point of some wondered if it wasn't provided by The Devil itself.
Here is one example among others.
October 9 1934, Marseille: the King of Yugoslavia is shot dead; the French escort start firing everywhere in panic. In the process two key people are killed or badly hurt.
First is Louis Barthou, a talented politician and diplomat willing to get his hands dirty. Guess who replace him ? Pierre Laval getting his first big political job on the way to Vichy and betrayal, that SOB.
Second key person is Alphonse Georges: Gamelin second in command and actually a much more capable commander. Georges however is badly crippled and will never fully recover. At the time Weygand succession at the head of the French armies is under way, and George had a chance. Instead of him, guess who gets the job ? Maurice "I have no brain left" Gamelin, with Daladier unflapable confidence (sigh) making him un-removeable until May 18, 1940 (facepalm)
In a sense, killer of the Yugoslav king also doomed France 5 years down the road.