> why are these sanctions here in the first place?
Initially they were a response to the Iran Hostage Crisis. Since the Clinton administration, the reasons have been Iran's nuclear program and support for groups such as Hezbollah and Hamas.
> It’s apparently ok for the US to have as many nukes as it sees fit, but not ok for others to have the same.
This isn't just a US goal. 190 countries have agreed to the Non-Proliferation Treaty.