Call it 'we have the bare minimum to win with':
The Martin news was actually a couple of days old as that was when his second 10-day contract expired. Just today he signed with the Atlanta Hawks. Whether or not the Bulls liked having Martin around, if they were to sign him again it'd have to be for the rest of the season. Similar with Mike James, whose role is gone now that Kirk Hinrich temporarily escaped that well again.
The Bulls may be bringing in other 10-day auditions, though probably will wait as long as they can before doing so unless Kirk falls back in the well or there's some other injury (impossible!). They are still razor-thin close to the luxury tax line even after the Deng+Teague trades: currently under $600k away, and that's not considering possible incentives due to Joakim Noah and Taj Gibson.