Money.
only one of those i could see SF looking into would be Cribbs. Harvin is good but is going to want too much money to extend. Baalke and, more importantly, Paraag Marathe are too good at the money part of things to tie themselves up on guys like that, they know they are going to have to pay Kaepernick, Aldon Smith, etc within the next 2 seasons. They'll keep building from the draft and supplementing it with free agents.
Going after a bunch of high priced big name guys doesn't work. Just ask the Eagles.