Most sermons don't make the transition to the internet gracefully. Never mind that sermons are, shall we say, largely disposable. And they are made to be heard, not read, even when they are delivered by being read aloud. Sermons that rely on eccentric delivery-- or often, simple oratory-- don't tend to read well in any medium.
On the web, Sermons tend to run long. Web pages aren't a good medium for long documents, especially long documents that resist being broken up in the way that HTML was made to support. Also, to be frank, a lot of sermons tend to be not worth reading (a common problem with internet information). Given the way that sermons are originally delivered to a mostly captive audience, there isn't a lot of impetus to tip one's hand and get to the point quickly. It's pretty typical to come across sermons on the web whose first screenful gives no indication of whether they are worth reading at all. I do not give them the benefit of the doubt.
But they reach their nadir in forums and newsgroups. I never read them there, especially when the poster has a history of sermon posting. These venues are about interaction, and sermons do not, in general, invite interaction. Those who repeated post sermons are unlikely to respond to replies. I suppose the principle at work here is that they post sermons because they have nothing of their own to say.