There has to be a collection department to recieve the taxes and enforce the law. Just allowing the states to send in checks to the treasury will not work.
But there will still be a need for an Revenue Service to insure that that state collection agencies are properly collecting, reporting, and sending in the sales tax as required by law.
That's called the U.S. Treasury. And how does that relate to an IRS which is designed to administer the income tax law with regard to individuals.
Your objection has no substance.