[davezatch]

Except that shipping is not necessarily obvious. There are several options (overnight, 2 day, longer) with different price points. Also, if you're a Prime member you get free 2 day shipping, but what if I'm prime but not logged in/using a different machine?

And setting a default shipping cost is likely to further confuse customers. E.g. if you show the cheapest option always, there will be a price bump at checkout, but you don't want to show expensive option by default because it raises all perceived prices.