Its the team format that causes so much of this sandbagging, as much as it is the individual. Captains look for advantages to give them a leg up on getting those key 3 points to book the win. You see it particularly in teams from small neighborhoods and apartment complexes. Its hard to field a consistent team with so few players to work with, and its too tempting to go out and recruit folks to "play down" so the team can win.
Winning at any level of sports is about finding an edge and exploiting it. The USTA seem uninterested or incapable of rooting out and eliminating sandbagging, so its an edge available to be exploited.