We all can see that on internet there are a lot of online shopping sites which have a lot of customers even bitcoin users also need paypal to shop online while they do not know that with bitcoin they can shop online easily without any exchange but they do not know about these sites. The reason is that these online shopping sites do not advertise their sites they even do not advertise on here which is the biggest bitcoin community and where they do not need any higher budget for advertising but can start a smaller signature campaign.
There are a lot of sites which accepted bitcoin transaction back to last few years when a transaction doesn't need a lot of time to be confirmed. Everyone could access those sites on Google of course, search it which took place in your city/country.
But, how much people willing to spend their precious bitcoin instead of just using fiat money to do a transaction easier and faster today? maybe just a few because many people think to saving their bitcoin as long term investment.
Steam can be considered an online shop, and they do accept Bitcoin. The payments are even instant..
For a clothings shop, or something similar to Amazon, it would be easy to implement BTC. That's because they're giving you a term of 2-3 days for shipping, time in which they can see whether the payment has been confirmed or not.
My guess is they do not want to accept BTC because of the highly volatile price.