I mean, they're not doing it for the American economy. They're experimenting to see how it affects their short and long term profits.

Why do i believe they're not helping the American economy? Because firstly, that is not what they legally holden to (ie, the stock holders). Secondly, and most importantly, Walmart is costing the country a lot by not paying their workers a living wage. So a job at walmart means another person on government social aid program(s).