It has been Buffett's experience that the best returns are achieved by companies with a stable history that don't need to change too many things to keep their competitive edge. Major business changes increase frequently lead to an enhanced chance of making a major strategic blunder.
Unfortunately the market seems to think the opposite is true, with huge amounts of speculative money pouring into stocks that are undergoing drastic restructuring because the market values action. Investors like fast moving industries like technology, flock to places where takeovers are likely and generally get so caught up in the idea that something may be new about the future that they are willing to overlook a very challenging situation going on at present.
When turnarounds do succeed the rewards can be excellent, but in Buffett's philosophy, which has two rules, "rule number one, don't lose. Rule number two, don't forget rule number one.", avoiding risk is fundamental to his success. Buffett does so well because he is able to pour money into many consistently good businesses, some of which have been absolutely outstanding. The market's affection for backing up a good story just in case the company can pull of a miracle is very much geared toward short term "killings" rather than long term wealth creation.