If there were other options than MEK and Komalar that could have greater influence to replace the current Iran regime, America will be happy to support them. However, I have seen no other popluar groups that may uprise and tak over the government. If you know any, other than MEK, Komalar, and Khatami's faction, let us know. Otherwise, there are no other groups that America can support to replace the current regime.
MEK/MOK has never been popular among Iranians at all.
Why the US government does not support the son of the late Shah of Iran? It is a big question in every Iranians' mind now.