Why isn't car shopping like food shopping?

I don't walk into the grocery store and start haggling over the price of bread or lettuce. There aren't two prices on tomato sauce; eprice versus MSRP. So why would I do that over a car?

Forty five hundred dollars is very close to 20 percent off.

The blessing. How lucky I am to be able to car shop. Many people aren't afforded the luxury. I'll try to focus on that fact as I push this process forward.