Frnd
Most probably the tool is not able to optimize the net for better transition because there is a dont_touch true on the net . You cant remove the attribute instead you need to set the dont_touch attribute as false on thet net using the set_attribute command, once it is made false the tool will optimize for transition violations, further during synthesis you can give preference to fixe drv (transition, capacitance) violations, so tool will give more stress to improve transition violation.