Poll pretty clearly shows the overwhelming majority of people disagree with you, so there's that, but more to the point, very often the discussion is based on the OP asking a question, and wanting various responses to it, not necessarily wanting some kind of 15-page debate.
In fact, with an awful lot of 15+ page threads, only a small minority (10-30%) of the posts in the thread will actually really be truly relevant to what the thread starter actually asked or said. So what you're actually reading through is often off-topic or essentially petty or largely-irrelevant discussions/disagreements between posters, often about very specific points of order (I've absolutely been part of this - most regular posters here have been!), which aren't particularly important or useful to know (as vital/amusing as they may be to the people involved).
There are cases where an important discussion is had, but frankly, far fewer of those go on for that long, and you see a lot less of "skipped the middle" answers, because when you come into the thread you can immediately see relevant arguments are still happening, not the "NO U!!!" that you often see after 15 pages.