The ECB has 2x the portfolio size as a share of GDP as what the Fed does. The Bank of Japan's portfolio is about 4x the Fed on that metric.

Why isn't the Eurozone collapsing, with interest rates skyrocketing and the Euro imploding?

Somehow Japan is still managing - despite a public debt & budget situation several times worse than the US - with a GDP per capita still on par with Britain, France, and just below Germany. And yet all the armchair experts endlessly predict the demise of the US.