the reason behind that is , most will install the clamp toward the end of the mag tube with a 2 point sling, it has been found by people just as Nordic, mesa tactical, clark, tacstar, they the sling pulls on the clamp and after continued use they aide in losing the clamp.
our mag tube have a sling plate that is close to the start of the mag tube that is has the most support.
That said if it is something that people want we may look at that at some point, but right now we have a large amount of both the clamp and the clamp with light rail in stock.