He also mentions the dominance of Google, Facebook and Twitter. Making a usable distributed alternative to these (or to Amazon, Airbnb, etc. etc. - even HN) is not an easy technical problem. It does not help that making money off such a distributed alternative is also not easy, but had it been easy enough to do, perhaps someone would have done it for free.
(Not to mention that for the average person, setting up a website and publishing something there is not an easy technical problem in 2016; most wouldn't know where to start. Personally, I'm not a web programmer but I am a working programmer and I can write a simple web app using a CGI Python script or Django or Rails, and for me setting up a website is fairly annoying in 2016. And anything involving non-static HTML is a PITA, and writing static HTML is no fun, either. The web is not the most pleasant thing, technologically, and this is one reason that a company amortizing the cost of dealing with the web over many users has an easier time than an individual trying to do something over the "bare" web without intermediaries.)