This kind of writing has its own rewards. It is just as valuable to the writer as the reader. Paul Graham makes the point that developing writing skills also develops your ideas. If you cannot articulate your ideas well enough for others to understand it, it is likely the case your idea is still fully undeveloped.
I mean, certainly there are plenty of things people want to comment on without writing a blog post on it. This discussion, for example. We're discussing this with relatively quickly written comments, not as blog posts that we spend a great deal of time on, put away for a day, come back to edit, etc.
It's also the case that time is limited, and there are some topics we don't want to spend much time on. It's common to see people argue that if you don't spend as much time on the topic as them, then your opinions on it aren't as worthy, but I can't really agree with that. It's very often used as a way to defend poor beliefs against obvious criticisms. You see it a lot with conspiracy theories. "You can't dismiss this unless you've read all of the writings on it!" But only true believers are going to subject themselves to dozens of books on a crank theory.
