The Iranian government are rather extreme theocrats, but they aren’t a suicide cult. They know that a nuclear first strike against Israel would result in massive nuclear retaliation aimed at annihilating Iran as a modern nation-state. They aren’t going to do that.

I think their primary reason for pursuing nuclear weapons is as a deterrent against conventional invasion, forcible “regime change” like what the US did to Saddam Hussein - much as Iran welcomed the removal of one of their national archenemies - given Iraq is majority Shi’a, a democratic Iraq is generally more friendly to Iran, although not all Iraqi Shi’a are pro-Iranian (e.g. Ayatollah Sistani, who is very influential, dislikes how Iran has politicised the religion) - but it raised the risk the Americans might try the same thing on them.