(Because they can decide what is constitutional or not)
Edit: I have more questions but for some reason I can't reply to your replies :(
With the current makeup of Congress, it is unlikely so the USSC holds significantly more effective power than if it had a functioning Congress.
The two-thirds threshold you mention is for Congress to propose amendments.
Edit - wow this is actually true. From white house.gov:
> An amendment may be proposed by a two-thirds vote of both Houses of Congress, or, if two-thirds of the States request one, by a convention called for that purpose. The amendment must then be ratified by three-fourths of the State legislatures, or three-fourths of conventions called in each State for ratification
Kinda weird to ask, when the answer is five seconds away plugging "US constitution amendment process" into a search engine.
> wow this is actually true
Not sure why you're so surprised about it; consider that the threshold for overriding the president's veto of a regular bill passed by Congress is a two-thirds vote from both the House and Senate. It seems like the bar for amending the constitution should be higher (significantly higher) than that.
Besides that, not involving the state governments at all when amending the constitution feels like it would be a bad move, in a country founded on the idea of strong state leadership and a comparatively weak (though not as weak as some of the founders wanted) central government. Certainly our federal government is even stronger power-wise today than even the more strong-central-government proponents among the founders would have expected.
In a well-designed system, both have power over each other. That is certainly true in the United States.
The idea in US constitutional law is one of balance: we have three branches of government, and each are granted powers that can act as a check on the powers of the others. It's far from perfect in practice, but the intent is good, I think.
There's throttling to prevent rapid back-and-forth commenting as that can devolve somewhat; might be that. Try clicking the "X minutes ago".