Disposable income is income after tax. Europe has higher tax rates that the US, so this is to be expected. It also has better services. So what you don't see in this comparison is that in return for their higher taxes, they for example get free or cheap higher education and healthcare.

If the German government cuts funding for those two sectors, passes on the savings to people by reducing tax rates, and requires them to pay for those services out of pocket like the US, the disposable income may reach parity, but the people would probably be worse off in real terms.