You can still skip town and buy something at a random shop.

Not if the shop's not there.

The population of the Los Angeles Greater Metropolitan Area is 18.79 million according to Google. Yet I was unable to buy spare parts for a Shimano 105 Groupset anywhere within the city. The most popular line for the most popular bicycle part manufacturer in the world and the only place it was available was Amazon because everyone else doesn't want to compete on price. So they've got some Dura-Ace in stock at four times the price because it's a luxury item people want to fondle.

Sure- any number of shops could get it for me. They're on a 4-week turnaround because they've refined their supply chains to the point where they only get what they can sell. And they're not going to compete on price because if you needed it you'd buy it off of eBay - it'll show up gray market from Shenzen a week faster than they can get it anyway and if none of it fits, it's your problem for "not buying local." And yeah - some of those parts I had to order two or three times because Amazon doesn't pay their drivers enough for them to not have a "not feelin' it" day. So in the end you can't "buy something at a random shop" you have to find it online, make sure it isn't fake, wait a week, and then go five miles to the nearest Amazon Locker because at least there? You know it'll likely arrive.