Part of the problem is that, while Marx writes well regarding the economic flaws of capitalism, he isn't as good at writing about the politics of change.
When induced by the body politic, we see that some of the economic surplus can be reallocated to the workers provided there is political pressure. It can come in the form of state backed rights, progressive taxation, and even direct welfare payments.
It probably isn't the perfect system Marx envisioned, but enlightened liberalism is able to make subtle shifts over time in a way that absolute monarchies can't.