You can defer taxes on investments for years until you liquidate the investment. Buy stock in a company or fund that does not pay dividends. You do not owe taxes until you sell the stock.
The US government's interests are constrained by the US Constitution, which limits the type of taxes the government can impose.
Sixteenth Amendment: "The Congress shall have power to lay and collect taxes on incomes, from whatever source derived, without apportionment among the several States, and without regard to any census or enumeration."
Words have meanings, and a loan is not "income".
(the collateral in this case is all of the borrower's future income, given that student loans cannot be discharged in bankruptcy).
What if the student loans are turned into beer?
Should they then be considered "income"?
If you think this sounds facetious, you've never been on a college campus the day the student loan checks hit the banks.