Why would Iran nuke Israel? They know they would immediately get hit with nukes from all the Western countries who own them, including the remnants of Israel, who have a well-known deterrent strategy called the Samson Option, according to which they fire off all their nukes if a country has invaded them and/or destroyed a part of the country (for the Christians on here who I assume don't read their Bibles, Samson killed thousands of Philistines by pulling the temple down on them, killing himself in the process).
There's a reason why Iran has not invaded Israel or attacked the US. They know they cannot win that conflict. They use indirect strategies, like putting pressure on Israel through proxies like Hezbollah and Hamas.
It's quite similar to our own approach to Iran. We've wanted regime change for 40 years, but we know we cannot successfully invade Iran without unprecedented American casualties. So we work around the edges with our own sanctions and proxies to put pressure on the Iranian regime, hoping it will collapse in on itself.
Israel wants to drag us into a war because they have very little to lose. They know that Iran can't "win," at least decisively in a way that gives them more power. They also know that nobody can possibly go into Iran and take control without massive, massive casualties, which the IDF cannot sustain. That's why they want the US to get involved. Israel sees American soldiers as cannon fodder. They want us to do their dirty work.