simple, Germany had no economy, no money, You can't get what isn't there. Because of the Treaty of Versailles and it's terms, Germany found it impossible to get back on it's feet. Because of the terms of the treaty Germany had no growing industry base. While other nations moved ahead Germany was left behind and was faced with making huges payments.
I think you misunderstood what I wanted. You said Germany suspended them in 1921. That's like signing a cease fire and continuing the fight after a few years and the other side lets you without protest (Hello N. Korea). You also said it lasted through the end of WWII meaning that as the rest of Europe watched her grow in Military power, they ignored the fact that she owed the huge restitution payments. If this is the case, then one could also argue, while devastating, the treaty of Versailles apparently had no teeth, so wasn't as significant in the starting of WWII as thought.. If 2 years after it's inception, it couldn't control a nation devastated by war, what makes anyone think it could restrain Germany for any length of time?
I might be missing something, but these were the questions in my head and the reasoning behind them in short.