The NFL recently changed their league year calendar to accommodate veterans looking for new teams. The old rules stated that anyone signed before June 1st would count against the league's compensatory pick formula, which scares teams away from signing role-playing free agents until after the deadline.
This season, that date has been moved up to May 12th (today), which gives these vets a chance to sign with teams, get into facilities, and start into the teams' offseason programs a few weeks earlier than normal. This, in theory, gives them a better shot at making the final rosters.
This means that you can expect to see the final wave of free agents still out there start to get scooped up by teams looking to add depth or a few key roles. It also means that free agents like, say, Tarvaris Jackson, can finally start to get an idea of what his value will be on the open market before re-signing with the Seahawks. Free agents that re-sign with their own teams do not count into the comp pick formula, so Jackson is evidently just playing the waiting game in the hopes of gaining some more leverage in terms of what he's going to get paid this year in Seattle (if he stays). If he finds some interest elsewhere, the Seahawks may be willing to up their price in order to have a dependable, veteran backup behind Russell Wilson.