To be fair Sobers was much more effective when he bowled fast-medium in his early days, but his batting soon took priority and he started messing around with other styles, a sort of more effective Tendulkar. It's almost impossible to be a top-class all-rounder with both bat and ball because, after all, we are only human! Batting takes a lot of concentration and having to bowl afterwards was an added strain, so he started bowling spin which was less tiring. I have no doubt that just as a seamer he would have got a place in the side, but he tended to bat so long it put too much of a strain on him and he had to adapt, even though his seam bowling was more effective. People tend to work on one side of their game more than the other, take Kallis who is the best all-rounder in the world at the moment, his batting has taken off and he's bowling less now and is mainly less effective than he was a few years ago, but you don't want to wear him out. Also if you have just batted for a long time you find it hard to focus on bowling, and also having less overs than normal can affect your performance, since it's harder to get into the swing of things when you are only on for short spells.
