One of the major factors effecting marksmanship in that exchange was that the bad guys were in a dark shaded area (under a tree IIRC), while the good guys were all highlighted in bright sunlight. Moreover, this caused the good guys to be squinting and shooting more or less into a black hole in which they couldn't clearly see their targets. In other words the bad guys had concealment in the open by virtue of the sun/shade circumstances. Not the only factor by any means, but a major one nonetheless.