Is there a functional reason, like helping with rainfall or snow, or is it more of a cost issue?
Are there decks that are solid pieces of bonded wood?
To let rain water drain off the deck, and prevent pools accumulating in joints/cracks and causing mold and rot.
It also lets a deck dry faster to avoid slippery surfaces. Further, it spreads the dripping water over a broader area and allows it to soak into the ground underneath faster and more evenly, avoiding heavy drip lines at the edge of the deck.
While bonded wooden sheet decking could be theoretically possible, I have never seen it, and why would you want it?