You're missing the third party of that equation: convenience. The flip side of customer service is having to deal with a stranger whose job it is to make money off of you and explain complicated things to you.

Amazon isn't successful just because it's cheap, the fact that you can reasonable expect for anything you order from them to be delivered to your house in a couple days, and that if anything goes wrong they will actually care about making it right, is why Amazon beats out other online stores in addition to hurting local retailers.

In my interactions with salespeople do I want to receive great customer service? Of course. But I'd much rather just skip the sales person completely in most cases, because they are in the way of my convenience. You have to establish a rapport with them, explain what and why you want something, figure out a negotiation tactic, deal with getting approval from them, and the manager, and financing.

For someone that doesn't know what they want, a good, informative salesperson can be vital, but not the kind of sales people that typically get hired to sell cars. They are sales people, working on commission, needing to sell what they have on the lot to pay their own bills. Its not up to them to be an unbiased source of information, from all we known and see the most successful ones are the ones that take advantage of the misinformed rather than helping them.

So yeah, avoiding the dealership experience completely is what I think most people want to do. Dealerships did it to themselves with decades of their previous business model, and the only real reason they haven't been completely usurped already is the myriad of legal restrictions that exist to prevent manufacturers from selling directly.