Any more pressure could possibly snap the lines entirely and force a retreat but Iran may be chosing keep them barely supplied to put political pressure on Trump instead.
Could also be a situation where if they collapse the supply lines, the US will escalate and will regroup and reorganise better supply lines. This war is more focused on attrition, so slowly bleeding the US dry through inefficient supply lines like this probably does more damage than a big loud strike on them would.
GO HOME GI