Yes, anyone can make a website, anyone can accept payments, and anyone can promote their site and reach an audience.
(and it'll take time and money; people are free to use another service or build it themselves - isn't this what a free market is all about?)
Amazon is the e-commerce juggernaut; Amazon.com is the 7th most popular website in the world. (4th in the U.S.)
The dominant player in a market sets the price. (apple & google play take 30%, uber & lyft take 20%, think amex/porsche/jetblue/nike...)
What is this? the 90's ? Anyone can set-up a simple free website and offer his services, of course a little bit of marketing and patience is still required, but for a smart man, that doesn't cost anything.