That seems most popular for HFT. 9-10X magnification and a 40mm objective limit the depth of field (DoF) such that, with parallax focus set around 23-25 yards, targets at 40 yards will be just starting to blur, targets at 45 yards markedly more so, which helps range finding. The same is true for close targets.
Going for a 32mm objective scope with the same magnification will increase DoF, so will be less useful for range estimation.