Cousins was all star level in 2017-18 for NOP, starting 48 games, averaging 25 pts / 13 rebs and with 5 assists. Since then, he has played for 5 different teams and been more in the 10 pts, 6 rebs range. He missed the 2019-20 season completely. So it is really 5 teams in 3 seasons that he played.
Cousins is an intriguing player for sure. But GSW, HOU, LAC, MIL, and DEN have all moved on from him after 30 games or less. Most of these teams are contenting teams, especially the most recent (LAC, MIL, DEN), that could have used a solid back up big.
I don't know where Cousins' head is at. I doubt anyone does and that is the problem or the risk. A focused Cousins off the bench, even the diminished version of him, could be a good thing but it is really hard know what you are going to get, or for how long.
I suspect the Celtics want someone more reliable or more predictable for their insurance big, even if that means less potential ceiling. The Celtics may still grab him. It does not appear he is coming off the board anytime soon. But it seems they are seeing who else may get released or otherwise become available. We have the TPEs that would allow us to complete a trade for someone a team needs to cut anyway to reduce their roster.