When you say someone is blind it carries connotations of barely functioning on a normal level, possible incompetent when it comes to tasks sighted people have no problem with and generally not up to par, whereas using the newer terminology it's implied that this is an otherwise normal person with full mental faculties who is having some problems and not a person who is less than normal because of their deficiencies whatever they are, an attempt not to push them down by giving a label that implies inbuilt problems on the mental level.