Also, it's said that Eastwood just shoots the script, and that's the movie. More experienced directors rely more on their gut and feel free to shoot things differently on set, and leave footage on the cutting room floor.
It's not that he's a bad filmmaker, just that he's not as good as he could be. Bloodwork was really awful, and I doubt Invictus is as bad as that was.
I wish Clint had a bit of Sergio Leone's continental cynicism or irreverence or ambiguity or whatever. Clint's the good cowboy, the man in the white hat, but what Hollywood sees as "good" and "bad" has changed over time. The roles he played in other people's movies were more complex and ambiguous than his own films are.
Hitchcock supposedly almost exclusively shot what he had already storyboarded. I think Clint works in a similar if slightly more conceptual way.
Sometimes like Bloodwork and maybe Invictus he is working with weak material, and even tinkering won’t help that.
When he works from strong material, why bother shooting other stuff? He also brings in great actors and that allows you to work quick when everyone knows what they are doing.