you need much, much better UX (User Experience). Millions of people are now using facebook groups thanks to its easy real-time comments and well thought out threads. Good luck having that on your blog.
Alternative software needs to be vastly improved and centralized(1) for this to work. This is the problem, nobody is incentivized to fix it, so there you go. You get monster proprietary platforms still growing.
(1) Some people think decentralized platforms is the solution - it totally isn't. It is bad UX. They first build it, then find out it doesn't work, and this repeats. Why should everyone take the hassle of hosting their stuff? Plus, syncing everyone in a single feed is not an easy problem. I guess email is the outlier here.