A) Because we're a bunch of nitpickers and with this level of dedication, it would take so long to "fix" any movie ever made and B) It didn't take six years to "fix" everything in ESB it took six years to alter a whole bunch of things and to fix a few others, which could be considered mistakes - just take the clip Adywan just uploaded - while it certainly looks great, out of like a hundred altered shots, there are very few, which could be considered fixes of some actual mistakes, the rest is just enhancing shots, which certainly weren't actual mistakes in the original.