Because the retail price of a new engine (short or long block) plus labor to transfer all the "fiddly bits" - sensors and auxiliary components - would cost significantly more than the vehicle is worth, that's why. The $4000 quote for the used engine is already what the entire vehicle would be worth even if it ran OK! A vehicle with 200,000 miles, E or not-an-E, is basically scrap metal, value-wise.
Having just done the research, my advice to the OP is just find somebody to who will give you a few bucks for it for the scrap value. It's just not worth dumping that kind of money (and time, and effort) into. Take the money from the scrap sale, add that to what the new engine would've cost you, and get something with fewer miles on it that's not one step away from the crusher.