Why couldn't sauron make more rings of power?

[Tuor Turambar,Cursed by the Valar]

He could have created more Rings after he created the One Ring, but no one would have accepted them.

Well, he might be able to ensnare some easterlings or some haradrim.
I think the question now is whether making more Nazgul like people would make the original Nazgul less powerful. Any ideas? I think it is an interesting question, even if no one else does.