On top of that, some percentage of users who do contribute content are just recycling/reiterating content they've seen have success in that community before. Reposts, memes, predictable opinions, etc. The number of people who actively create the culture of an online community (and, I suspect, offline communities) is pretty small.
Where does the novelty element start, though? Someone could come and argue that your comment is also predictable, as is my reply below it.
Thats what is most interesting about human innovation and creativity in general. There are very very very few original ideas out there. Almost any idea anyone has had, a large number of people have had it. And most innovation is just tiny tweaks to existing formulas, over time.
In fact, if you understand the backstory behind most innovations, you realize it really wasn't all that impressive. There were many proposed models for flight before the wright brothers. They stumbled upon the right mixture. Modern day car fuel engines have essentially evolved over centuries of perfecting "torches" (fire and gas to create heat)
The people who make history are simply the first ones to act upon these thoughts. So, you become a content creator/culture setter, by simply being the first one to vocalize your thoughts.