Because this war is driven by Israel, not the US. The destruction of Iran, no matter what the costs for the world, is seen as an existential matter for the current Israeli government.

But, destroying Iran without using nukes is not a Job Israel can do by themselves, they need the US. And while the Democrat establishment (although not the base) don't see an issue with supporting Israel activities in Gaza, the West Bank and Lebanon, a war with Iran was not something the Democrats would agree with.

So, they had this window of opportunity with Trump, before the midterms, and they acted.

We may not agree, but under the point of view of the Likud, it makes perfect sense.