The 16th amendment plainly restricts taxation to income. Same reason there isn't a Federal sales tax or property tax.

No, the 16th Amendment expands taxation to income; there was some dispute at the time over its legality. (https://en.wikipedia.org/wiki/Pollock_v._Farmers%27_Loan_%26....)

Article I establishes's Congress's fairly broad taxing powers.

> The Congress shall have Power to lay and collect Taxes, Duties, Imposts and Excises, to pay the Debts and provide for the common Defence and general Welfare of the United States; but all Duties, Imposts and Excises shall be uniform throughout the United States.

https://www.law.cornell.edu/wex/sales_tax

> The federal government has not enacted a national sales tax, although it has the constitutional authority to do so under Article I, Section 8.

There are federal capital-gains taxes. (I’d be fine with just treating wealth gains for anyone with more than $100mm as income, too.)