[rcpt]

Sometimes there's only a single tax allowed. Like in the US the federal government can only tax income unless they change the constitution.

LVT as the single tax would be much harder to repeal.

[sokoloff]

This is close to, but not entirely, true. The US federal government also has the power to levy direct capitation taxes (taxes that are effectively constant per-person without regard to any other factors).

In practice, those taxes are impractically regressive, but the federal government does have that power under the Constitution.