I now buy most of my bicycle supplies over the internet.
There are a few reasons for that.
I've been doing all of my own bicycle maintenance since I was about 10 years old. So, I have most of the tools I need, and I don't need to go into a shop to ask them to put on a new chain or replace a brake cable. And, now with the internet, there is a better source of more accurate information at the tip of my fingers than any store employee could have. With the nearest store, say 10 miles away, and the best store (I think), 15+ miles away, I stock many of my basic needs such as spare tubes.
I do like browsing in stores such as bike shops... or at least I have in the past. And, sometimes I will buy some trinkets when I do. I usually ask to be left alone as I look things over. However, if I'm actually shopping for something specific, then it is often that one item, or nothing. Unfortunately they usually don't put the most interesting stuff on display.
I find it very frustrating when I go into a store and they don't carry the one item that I'm looking for, and I refuse to spend hours hunting across town when I know I can spend 5 minutes in my living room and find it, plus a dozen similar items to choose from all at half the price I can buy it for at any store.
Sometimes I like to do some research before making a purchase, which is also at my fingertips at home.
I certainly don't need to pay somebody to go onto the internet, buy it, ship it to the store (where I have go return for a second trip) and to mark it up.
I suppose a store makes a decision to either carry a little bit of everything, or just the "mainstream items". So, when I go into the store looking for a little bit obscure brake pad, and they don't have it and claim that it can't purchased anymore... well... it just means that not only do I leave the store empty handed, but I don't come back very soon.
Most of the E-Bay sellers are just small businesses, no different than anybody else.
I do like the idea of small stores where one can find replacement parts in the middle of a trip without having to get stuff shipped. Yet it has its limits.