I don't know why the selectors pick who they do. You have to ask them. As David Boon once said as a function I was at many moons ago: "there are 20 million selectors in Australia, but only 4 opinions count" (there were 4 selectors at the time he said it). Katich may have been in the eyes of many, a better batting option than others, but that simply doesn't automatically mean that Clarke somehow, single-handedly, sabotaged Katich's career.
I'm not Clarke fanboy, and think its time for him to move on himself. He will never fully recover from his long term injuries and will not get better IMO. But for some reason there seems to be so much taken as fact by some, when, in reality we don't know.