It’s just a fact that in the US that any item over a particular cost is not a fixed cost item. There’s always room for negotiation. It’s not awesome for those bad at haggling but it is what it is and it’s not limited to cars.
Honestly, if you're paying cash, it's not a big deal. I bought a car a couple years ago. At the time, there wasn't really any point in haggling on the car's price given how in short supply everything was. I got them to toss in some extra trade-in to cover the "factory options" on a car that wasn't even built yet--with the proviso that they had a deal if they agreed to it. I took a very discounted extended warranty which may or may not have been a good deal but it was cheap.
The whole thing, including test drive, took me maybe 30 minutes. I said "no" quite a few times but it was hardly a pressure-packed negotiating session.