Because that’s how they roll:

Iran’s supreme leader, Ayatollah Ali Khamenei, has said in a televised address that Iran will expand its nuclear program and will not negotiate with the United States. Ayatollah Khamenei also said that Iran would maintain its close alliances with militia groups in the region that it uses as proxies.

They say they will manage to evade the sanctions by signing a deal with China, which can fill all its international trade requirements.

(NOTE: The sanctions have done what they were intended to do. Iran’s economy is in shambles.)