5 yrs after hairline lowering and hair did not grow, what could have caused this and what are my scar removal options? (photos)

It appears that your scar was placed few mm in front of hairline and that incision was not zig-zagged as usually needed with this technique. It may involve some hair loss as well? Another excision placed exactly 1-2 mm inside the hairline with oblique incision to preserve some hair follicles (so that hair can grow through the scar) will shorten your forehead and result in better scar. I am not sure whether hair grafts would be a better solution to hide the scar and lower the hairline? Good luck.