Why do the 49ers want to keep alex smith ?

The guy is a horrible qb that looks lost at times he also has 2 first rd picks on his o line plus crabtree gore Westbrook if he comes back and some ok wideouts Patrick Willis can only do so much for the d but they get it done why can't the 49ers just cut smith and start kapernick and bring in a vet like aj feely to mentor him