Why Do the Good Free Agents Get Snapped Up so Quickly?

So, when starting a new season in career mode and going to the 'search' tab in the transfers area, it sems that, even on day one of a new season, all the really good free agents have all been assigned to other teams.  I'm talking about seasons 2 and beyond, in a career.

Does anyone know why this is, or am I searching at the wrong time?  If so, when should that search be done?