It wouldn't. Say someone in the US buys something made in China - how does that increase demand for labor in the US? There's some marginal US labor required for the last part of the transport, but that's it.
Thee last part of the transport is not marginal in the real world. Increased local consumption drives transport, retail, marketing, etc. etc.
Real life economic modeling is not a simple supply/demand, widgets made/sold chart.