It’s a pretty standard process to have some parts installed “loose” and tightened at a later time. It could be to ensure fitment, add rigidity or even just to protect the mating surfaces from the elements during transport.
Also it’s probably not just because Boeing is gonna open them up that they don’t fully secure them. I haven’t seen the specs but it’s quite common to have a reinspection requirements when disassembling something that was fully installed for stress and damage.
Pretty much nothing in aerospace is left to communications. The assembly manuals are not just complete, they are painfully exhaustive.