Hey Fuzz Force, thank you for reaching out to us.
You are absolutely right, currently the game is kind of hard solo.
Wild Woods was designed to play with friends but in the future we will try to concentrate more on getting everyone satisfied.
The reason why you have to be behind the wagon to get wood into it is that this creates more coop situations, because if you play with others you can throw stuff to other players and they can throw it into the wagon. One player could stay behind the wagon and another one throws wood to him.