If Israel were going to do this, they needed to ensure that what they had planned for years (recruitment of spies in Iran, building of the drone factories in Iran, infiltrating the IAEA) that it could be completed.
I know why they did it there's always been a struggle between Iran and Israel to be the dominant power in the region. Israel wanted to cement its hegemony (being the only country with nukes), that's why it systematically attempted/managed to destroy or weaken Hezbollah, Hamas and Syria.
The was always to destroy or restrain Iran, whether through sanctions or military action. I think some planners were hoping for a situation similar to what happened in Syria in December a complete collapse and the installation of a government more friendly to the West.
It was predictable that the negotiations would end up in a war as the terms offered to Iran (no enrichment, curtail it's missile program) are something that no sovereign country could accept.
Therefore it was predictable that Irans response would be severe if the decapitation strikes did not work. Netanyahu chose that time as he had just survived a vote to dissolve his government, but were they ready?
Now no one knows where the 400kg of Uranium is (if not destroyed), no one trusts America. Air Defence missiles are depleted and all Iran had to do is survive, which it has so far. Now the Iranian Defence minister is China viewing Chinese military equipment and Iran has checkpoints internally to catch any spies.
I'll post it again as it was laid out quite clearly, read this especially chapter 6 "leave it to Bibi"
https://www.brookings.edu/articles/which-path-to-persia-options-for-a-new-american-strategy-toward-iran/