Or why Belgium is nearly 4x that of Germany. Or why Italy is 3x that of Germany. And so on. It's very clearly a problem that specifically has to do with Germany. Even South Korea, which has only started to become affluent in the last two decades, is well ahead of Germany and Sweden (and the US median as well).
You're also making the excellent point that Americans should be far worse off than Germans and Swedes, because they should be going broke constantly due to medical bills. And yet the American median wealth is still higher.
The US spends as much on its welfare state as a percentage of its economy, as what Canada and Australia do, and is just behind Switzerland.
The median American receives healthcare through their employer. That directly detracts from their income potential, and given how expensive US healthcare is (typically 60% to 80% more than other developed nations), it detracts in a very big way. By your way of thinking, we should account for that massive gap in cost of healthcare and how it impacts income figures (which impacts max savings potential). It's certainly not fair to account for Germans paying into taxes for eg healthcare, while ignoring that Americans lose out on income in the relationship with their employer due to the immense cost of healthcare in the US: that is the tax.