That's because the state governments control and maintain the public roads and because any power not specifically granted to the federal government in the Constitution belongs to the states.
Each state handles laws concerning drivers licenses .
Yes.
The Secretary of State's office issues the drivers licenses.
No. When you apply for a drivers license in your new state you are required to surrender your previous license.
New York
Missouri
Basically, it's an identification number issued to you by the state.
The state DMV issues licenses.
Yes, a person will get a suspended drivers license with DWI in any state.
ALL state's laws prohibit this.
Marriage licenses are issued by the state. In most cases the state has directed the county handle the registration.
You cannot possess drivers licenses from two states at the same time. There is a national register of drivers licenses, and each state checks that database to be certain that you haven't been licensed before or concurrently.