This isn't exactly true. The EU is opposed to Iran's aggressive policies in the region (e.g. in Yemen, Syria, and now Hormuz) and its continued development of ballistic missile technology. They're just content with the 2015 nuclear deal as a starting point, whereas current US policy is not.
It's also worth noting that the EU disproportionately benefits from oil purchases from Iran relative to US so they have their own political self-interests factoring into their decision.