The big name free agents are likely to land elsewhere and the Celtics have a lot of money they could spend. Thus they have been attached to a lot of 2nd tier free agents in the rumor cycle.
The thinking is that teams like the Celtics might be willing to overpay free agents this summer knowing that the cap will explode in the next few years and big deals this year won't look so bad in the future. Also, most teams will have more cap room in the following summers, so we might want to lock in guys while we've got some advantage right now.