in my experience, their slacker types are very good at generating alot of "management noise", so that anyone not aggressively paying attention can be misled for months into thinking actual work is being done.

and then, once the con becomes obvious, the exec would need to come clean that he personally failed at his supervision duties, and wasted possibly hundreds of man-years. going into confrontation is risky, just from the corpo politics side, and then there's the threat of accusations of racism, so its a very unpleasant uphill battle. unsurprisingly most chose to cover it up instead, and pretend everything is fine.