Carotid artery surgery for lack of blood supply to the brain?

Carotid for stroke: Mostly because the artery has plaque and that can become loose and cause a stroke.

Unusual: Typically carotid artery disease causes stroke or TIA by embolic phenomena where a plaque rupture induce clots that travels to the brain. Due to extensive blood flow to brain from two carotid arteries and two vertebral arteries, it's unusual for chronic occlusion in one artery to cause symptoms but it can especially with more proximal occlusion , this can be corrected with bypas surgery or stent.