I think the reason that can work is that (the vast bulk of) Walmart is entirely dedicated to executing on a single, very well defined (and easy to measure) task

I think the reason that can work is that (the vast bulk of) Walmart is entirely dedicated to executing on a single, very well defined (and easy to measure) task - their supply chain. Unfortunately, few problems in the world are like that, and that's why large companies (and governments) fail to address them effectively.