I wouldn't want to buy a random bike I haven't test ridden unless I am super confident in the geometry and how it will ride. Plus I would rather not support Billionaire Jeff Bezos.

However I am curious what you are looking for that is high end from Amazon. All the bikes I have seen on Amazon generally come in with problems, one had a fork that was crushed in the box (the box was undamaged) others have had similar damage or missing parts or are just poorly made. However maybe things have changed a little at least with bike quality, the way they treat employees and ruined local business hasn't.

As ChesterCounty said you lose out on support and support can be quite handy. As someone who is the warranty manager at a bike shop and also deals with a lot of customers those who don't have support screw themselves and end up spending more when they could have actually had warranty take care of it.

We had one customer recently who came in took all of our advice and time and then bought the bike online from a curtain and duvet seller on eBay. They had a very expensive issue that normally would have been covered under warranty and been really easy to resolve. Now they had to shell out big money to replace something and made us like this customer a lot less. At this point they didn't save much and really hurt themselves trying to be cheap.