They have secured a place in the minds of people as being the only place you can get anything - or, get anything conveniently, I guess. I hope there's still physical stores out there that do e.g. airsoft goods. The real "problem" is of course that consumers are then faced with real consumer prices, where they have to pay $15 for a good pair of safety glasses instead of $1.50.
They've gotten good enough at SEO that it's honestly hard to Google for alternative or niche vendors.
Unless you're plugged into the community for the activity enough to know the reputations of big online vendors, you've got the same problem of low quality, counterfeits, poor fulfillment, payment processing, etc.
I can't remember the specifics, but with the certain model I wanted, at a reasonable price, and with shipping to Sweden I'd like to remember that Amazon was the best option. Regardless, although my last sentence might've been a bit dramatic, the point of the anecdote was to share how Amazon lost me as a customer because of their counterfeit problem.
The first search result for "airsoft safety glasses" is [1], which shows me Danish prices and a delivery cost to Denmark.
Amazon might be easy, but knowing their products may be counterfeit, the company pays next to no tax, and has underpaid staff on awful contracts, I've not bought anything from them for years.
I must qualify what I said by saying that I've found this much harder the more specific I need to be. I could find 0 results for short M3 screws when I searched domestic sellers a few weeks ago. No hardware- or electronic stores carried them. One had them listed with a 3 month delivery and at about $3 each. After that hour+ you Amazon it, without putting hours into finding it in other countries who's languages you don't speak.
Airsoft glasses is something I can find in any mall here.
We're pretty well of the beaten path of Amazon here, but I had a similar need (#1 slotted flat-head brass wood screws) that McMaster-Carr didn't sell a little while ago and found them on microfasteners.com. It looks like they stock metric machine screws as well.
If nobody goes to retail stores to _ask_ for a specific type of security glasses, how will they ever know to stock it? We, the consumers making Amazon's monopoly.
While security glasses are something that you will hardly find in a typical mall retail shop, it is something, that shops with tactical gear do stock. They also haveh a clerk, who can give you an advice for your specific needs.