The problem here is the following:
1) It is very difficult for most of the people to manage domain name, hosting, cms...
2) There is a mental barrier for people: "I don't have anything important to say other people. Own site and domain name automatically means that this is serious, that I have something important to share with the world. But I don't!". From other hand, account in twitter or FB doesn't require be serious! I can repost stuff and memes by just single click! I can write post something like "now I am drinking coffee in hipster cafe! it's cool! :))))" in twitter, but it is shame to use own domain and hosting for such kind of posts.
3) If I want to quickly find readers I will use social media. Because, it is very easy to follow people - just one click! Most of the people don't know about RSS.
4) Twitter as well as FB try to push people write something. Text form for making new post is in the same page as feed. In the case of indieweb the feed and post making form separated. So, I will think twice do I need to post something.
5) Comments. A lot of different formats of comments in the big web is the thing which is the barrier for commenting. In the common wordpress comments there absent identification. Anyone can write comment with using my nickname and my blog address. So, I install the Disqus comments in my blog. This is not ideal solution, but this is popular, and this is the thing what really connects "indie web".

Sorry for my English, this is not my native language.