When I was disassembling it one of the 4x4s broke (Debnw)
Pressure treated (PT) lumber is stored & shipped wet to prevent warping and splitting when nailed/screwed, and also so the deck/structure shrinks around the fasteners to make the entire assembly tighter & more stable.
Hidden flaws, burls or swoops of grain can pop apart on their own once the drying action gets fully in gear, especially buying the PT flavor-of-the-day from a big box store.
For structurally vital bits a private lumber yard that supplies the trades may be more expensive but usually has a better grade on hand and will provide their best if you explain where its going to be used...
Anyhow - Debnw & purman -
great photos & thanks for sharing. Wish I'd gone the crane method, next time right?