The United States does not recognize Taiwan as a sovereign country. The ROC is not recognized as the legal government of Taiwan. Read the Taiwan Relations Act and see state.gov/s/inr/rls/4250.htm where this is fully clarified.
So, the question arises, why should US citizens be allowed to renounce US citizenship to obtain ROC citizenship, when the ROC on Taiwan is not a legal government, and Taiwan is not a sovereign country?
If you are a US citizen and would like to write a letter to the US State Department about this, I have composed a draft letter and posted it here:
Download this three-page file, and insert your name/address data, as well as the date.
Send it in to the address of the Department of State as indicated.
(It is recommended that you get this file in a new window . . . . . . because sometimes downloading doc files makes WINDOWS become unstable . . . . . . ) I think the programmers at Microsoft should look into this problem . . . . . . . . . .