I imagine if the slightest thing seemingly goes wrong it could have a snowball effect.
People rushing in panic in any direction out of fear or curiosity.
Landing a plane that size is hard enough but with all the mass tumbling around makes it even more unpredictable.
The seatbelts aren't for your safety allone, they also keep your mass in place so the plane doesn't react unpredictably.
Also a big plus if during the turbulences you're not getting flailed by the whirling around extremities of a beltless corpse or getting crushed by its torso.
Remember, force equals mass times speed and there can be a lot of accelerstion during turbulences.