Will of the Nazgul/Creating More Nazgul

[Hakon]

This section of the Appendix also states that Dwarven nature provided a resistance to some of the effects of the Seven and, as a result, they could not be reduced to wraiths or enslaved to Sauron's will and their lives were not extended. Nonetheless, the Seven did have evil effects upon the Dwarves because Sauron assisted in their forging.

Well as Mithdan said earlier according to the Appendix the rings would not have turned the Dwarves to wraiths. So why would Sauron offer the three rings back to the Dwarves? It seems kind of pointless if he had nothing to gain from it.