Why do you think people in R&S often substitute their own question for answering rather than just ignoring it?

If find it interesting that people will bother to "answer" some question of their own preference (substituting it for the question actually submitted) rather than simply moving on to another question. Why do you think this happens? Is it because such people come here to promote their own belief system OR because they think that this will "frustrate" the person sincerely seeking knowledge by asking a question OR is the reading comprehension skill of the average person on this forum as bad as it sometimes appears? (For example, someone asks a question about some aspect of Catholic theology and one can expect to read various "priests are pedophiles" nonsense that is simply ignorant propaganda.) So why don't people simply ignore questions for which they have no answer or which do not apply to themselves in any way? I've not noticed this tendency on many other forum categories.