i think partly why this is the situation is that we have this traditional format of church in which all of the expectation is on exactly one person in the congregation to teach the whole flock at least once and commonly three times every week -- so we have a class of people in the church about whom everyone in the flock is under the impression will have a constant stream of things to teach everyone else, while everyone else just 'spectates' until a handful of them one way or another take up the same vocation - with the expectation then being that they will go start their own church somewhere else and be the only person in some other congregation with things to teach and admonish everyone in it, and doing so constantly.
so we have all the spiritual wisdom supposedly concentrated in one or a small handful of individuals. that person is maybe not given revelation and inspiration 3 times a week, but they have to have a sermon prepared anyway -- everyone is depending on them because church isn't about being involved ((other than standing up at the proper time and joining in the organized singing)), church is about attending a rehearsed pageantry. what does this preacher do when he has nothing to talk about? he scours resources for prefabricated sermon ideas. so there's a market for that -- for pre-fab sermons. and where there's a market, there's fluff to fill shelves with, things with little substance or necessity, but possibly enough impulse buys to make them worthwhile. in terms of sermons desperate pastors purchase ((yes there really are places selling sermons to desperate pastors -- happy googling)) -- that means filler material. there's a market for it, so people produce it. that's how we get sermons focused on pointless details, IMO -- at least it's a major contributing force in their propagation.