That would be too confusing. Some states would adopt the law, some would not. It needs to be a federal law being the president holds a federal office.
It already IS a federal law. It’s the constitution.
We are a federal system. The feds can’t tell the secretaries of state how to organize or print a ballot or how to run an election. That’s one reason why we’ve got such a messed-up federal election system, hanging chads and all that.
The states run their own elections, period. So that’s where candidates can most easily be denied a place on the ballot.