I never understood the reliance on amazon. Its the internet, every category of item you could want has a bunch of manufacturer sites dedicated to it. "Websites you trust", hell are yall doing trusting Amazon.
Ease of use. For example, if I need something odd like a rack to hang bikes in my garage, I can find and buy one in 5 minutes and go back to whatever I was going.
Well dude that's the point. There's one site I can go and get something name brand and it's not necessarily going to be total garbage. If you've gotta Google something, then I dunno about you, but I'm checking a sites reputation before I give them my credit card information.
Point is there are a lot more steps and it's convenient to go to that one site that I know of hand and more or less can trust to not steal my credit card information.
Otherwise you might as well just go to a store locally and purchase it, but unfortunately that isn't always an option with everything.
If you're using Amazon, you go to Amazon, search for a bike rack, choose a bike rack, and order it with one click.
If you're not using Amazon and you don't know where to buy a bike rack, you go to Google/Bing/DuckDuckGo/etc, search "buy bike rack online", scroll through the results, opening website after website until you find what you're looking for, add the item to your cart, go to checkout, enter your name/address/card info/PayPal/etc, and submit.