If the proposal was to stop bombing if shipping is allowed free transit, is that not simply a return to where things were before this started?
If Iran accepted that proposal how does the USA explain to it's citizens what has been achieved?
Possibly more importantly how does the USA explain to it's gulf allies how this is a positive net result. Especially as there's been some suggestions that those same allies might be a tad miffed at being drawn into this without consultation.