One of the most frustrating things about academic Marxism is that it hypothesizes that “capitalists” do things like figure in the reproduction cost of labor.

It doesn’t? It never postulates that capitalists actively control the economy or do more than the bare minimum, on the contrary that they are bound to the laws of the market is one of the main points of marxism. That the cost of replacement factors into the cost of labor power is like the cost of replacement factoring in for any other commodity on the market. I highly suggest you read the booklet I linked, it’s very short.