Bank "money" issued by private banks and the Springer income tax go hand in hand. The purpose of the income tax in the 1860's was to drive people away from state & wildcat banks to provide backing/legitimacy to the Greenbacks. The current iteration of the Springer income tax is to provide a drain valve on total bank credit in circulation...this comes from the Article 1 section 8 clause 5 authority of congress to "regulate the value thereof".
Because you are not using the coin of the realm or other money issued directly by the Treasury you get "regulated" via taxation on your bank money income. Congress will get their seigniorage one way or the other. Using their coins and USN's and the they get it directly...use the banks money and the Federal reserve sends the Treasury its profits less 6% plus you lose a significant amount via taxes on bank credit. The choice(excise) is yours.
That stands out to me too. Really cannot have one without the other. Back when Americans were paid in gold and silver if they started taxing incomes 20 to 30% the theft would be fairly obvious. If Americans used paper money without an income tax then inflation would run very high, making that currency undesirable to the point they'd stop using it. The income tax draws off, or siphons the wealth of the nation while most of the populace doesn't even realize it. The wealth landing in the banks and government.