Because the Iranians have won and they know it.
The deal has been approved by the UN so sanctions are dead even if the US Senate does not approve the deal.
Obama has not been enforcing the sanctions for the last several years so the support for sanctions is a dead issue.
The Koran admonishes observant Muslims to provide their enemy with three warnings before an attack and the Iranians are following through on that obligation because it costs them nothing to do so since Obama and Kerry are 100% in the Iranian camp.
...about that three warning thing...
There’s a lot of unobservant Muslims out there. Or, do they consider their incessant threatening blather as warnings? That seems insincere to me, since there are so many of them, and they do not speak with a unified voice.