It's built into the premise of productivity, which ultimately derives from Locke's "labor theory of property" - if you put labor into something, you have a claim on its ownership. Later philosophers studying trade and economy built this up to mean: "if we can increase the quantities of things that are legible as assets, optimizing their production on the balance sheet signals increased labor productivity". We've been awkwardly gluing that concept onto everything ever since and trying to measure things like teaching, wildlife management and "designed in California" electronics as productive activities.

Locke was thinking in agrarian terms, about how farmers work the land, or how many ships a nation has in its fleet - he was building off the mercantilism of prior centuries which was also balance-sheet driven, but in a pure trading sense, with no connection between labor/ownership. That connection was important to ushering in coherent industrial policy, since it expressed the idea of importing raw materials and then exporting finished ones at a profit - when you come up with new categories of asset to sell, or optimizations on existing ones, the economy provides more goods and services, it experiences a gain in material wealth. The real limitation is that it's too localized: commons goods are persistently attacked by it because they don't figure into the balance sheet.

This is a great point. I'm reminded of Lakoff's metaphors. I wonder if these primitive zero-sum views of the worlds economy mostly stem from folks inability to even conceive of a less physical metaphor for the mechanism of exchange.

Locke can be forgiven, but his modern disciples less so.