It is being regulated...State by State.  

Federalism.

Cell phone usage on the macro end is pre-empted by the Federal Government; traffic control is a State function.

The only reason we have 21-year old drinking nationwide (virtually the only nation in the world) and had 55 mph speed limits is because the Federal government withheld money for highways if the States didn't pass those traffic laws.

You know, like Trump is threatening to withhold Federal money if States are going to be 'sanctuaries'.

Same threat; different issue.