Angle of the dangle.
Most of these problems can be attributed to the angle set between the bar and end links at kerb ride height. When the endlink length is such that the bar ends are horizontal and the angle is close to 90deg, little force is absorbed by the bar mounts and most is absorbed by the bar.
When you lower the ride height, have weak or sagging springs, or over work the suspension to the point of bottoming out, on stock length end links, things change dramatically. As the angle increases, more force is exerted on the bar mounts; in some extreme cases, particularly with adj height coilovers, the bar end to end link angle can reach 180deg and actually invert the direction of rotation, locking solid, hence all the reports of torn strut mounts and cracked bar mounts.
Adjustable end links are good insurance on modified suspensions.