Then why don't they investigate wage theft? Googling around suggests that the cost to the US economy is about the same as shoplifting (and I'm guessing individual cases could be much higher value than shoplifting). When was the last time a battering ram was used in pursuit of a wage thief? Or when was one even arrested?

To answer my own questions, police do not care so much about the "value" of the target. Their behavior is much easier to explain once you realize that their job is to protect capital.

Wage thieves don't flee. There's no adrenaline-pumping chase scene, nothing to tunnel-vision. It's also much harder to see on patrol.

I doubt it's the lack of adrenaline being the main driver for skirting away from "white collar" crime. More likely, the analytical and time consuming work required, and perpetrators who are much more likely to evade capture and/or sentencing, through usage of lawyers, accountants et al.

Also, the victims of wage theft are less likely to be "well connected" sponsors of political careers, while the victims of larceny are naturally more often business owners whom are more likely to have a "voice".

How much wage theft is treated as a criminal matter vs a civil matter?

Furthermore, cops aren't exactly skilled at digging out such things. Wage theft is something for the department of labor, not the cops.