I haven't seen Gobert associated much with the Celtics and this might be one of those "he has to get picked somewhere in this range" types of picks. Here's some of the explanation by Gioony.
A swingman who can play together with the likes of Rondo and/or Avery Bradley and a big man who can play with Jared Sullinger and/or Garnett are two immediate targets the Celtics' front office might look at on draft night. GM Danny Ainge also has never been one to shy away from swinging for the fences if he sees a talented player he likes, regardless of position. Rudy Gobert would add significant size and length to the frontcourt and is a prospect the team can afford to wait on as he continues to fill out physically.