Why is Ichigo always in Shikai mode?
According to the Bleach Wiki,


  Yoruichi Shihōin has stated that his Zanpakutō is a full-time released form type because of Ichigo's vast but uncontrollable spiritual energy upon generation of it, implying that it is simply a type of Zanpakutō that, without proper control of his spiritual energy, once in Shikai form, remains in said state.