But why would one guy spread it at just the fee spread and not 2,3 or 5x the fee?
It is not one actually wants to sell that much at 5.21 and the other wants to buy that much at 5.20. One is trying to push the price down to buy cheaper coins, and the other is trying to be a benevolent 'bitcoin savior' and prevent this. Seemingly protecting the market and his own investment. They two of them end up ramming these intimidation walls against one another hoping the other will get scared and remove the wall.
I think the buyer has been with us for a while. The seller is someone who got greedy at the price, and wants MOAR! Probably sold some and thought, "If they were $2 again, I could buy double". I think he is going to be an unhappy camper!