Enterprise was involved in a complicated timeline war from way in the future. When Nero took the Narada into the past he changed the timeline (e.g., he blew up Vulcan!). This means the future of that timeline was changed, which means the past timeline of Enterprise changed too (because its past was causally enmeshed with a post-TNG future). Nero changed the future. Enterprise was causally connected with the future. A huge chunk of the Enterprise narrative depends heavily on the time war (including character arcs, relationships, and the purpose mission of the ship). Enterprise characters were communicating, cooperating, and conflicting with factions from the future. Nero, by necessity, changed any and all aspects of the Enterprise story that depended on future events that Nero changed. And where is the "temporal police" in all this?