All history teachers teach the same history, all computers surf the same web, and all watches tell the same time. So why all the varieties of the same? Is it because there are good, bad, average? Or is each new iteration better than the preceding model?
In fact it is due to our differences. The teacher that you think is a great orator, I despise for calling on me in class. The gaming computer you love, I find bulky, heavy, and no better than a small, compact netbook. The watch that tells you your altitude, body temperature and pulse in extreme conditions, prevents me from getting a date. Companies target our differences through product differentiation. They increase profits, we get a product that fits our life style.
Many books, blogs, videos, and stories share the same ideas or messages. Why does anyone bother writing the same old thing? For the same reason we have so many choices when buying a watch. Each different book with the same message clicks with a different audiences. A new blog can present an old message in a new way changing your understanding and hence making the same old thing in fact novel.