Boucher is amazing, but his build means he's far too slim to guard some of the more traditional/larger bigs in the league - Nurkic, Jokic, Embiid, DeAndre Ayton, etc. Baynes has been horrendous and looks completely washed, Len is basically nonexistent on the offensive side and while he's a bit more of a presence on defense his play is still not up to par. So that leaves our 6'11 220 lbs toothpick as the only big we can rely on and because he's so skinny he gets bodied by bigger players and gets into foul trouble often.
Keep in mind our big rotation is so bad that we're already playing OG Anunoby significant minutes at the 5 position which is unsustainable for him physically and also leads to him getting into foul trouble against larger players. Baynes hasn't played in like 3 games and Len is averaging something like 5 minutes over the past 5.