If we're continuing the parking lot analogy, it's like there's an almost unending grid of parking lot after parking lot, and you can travel to any of them instantaneously and for free. Some parking lots have a lot of people, so you'd rather go there if you want to be heard, but nothing is stopping you from setting up shop in an empty lot, and nothing is stopping people from visiting your lot.

Now, given that major social network advertise pretty much everywhere, this might not be an entirely fair analogy. Some parking lots have ads for them posted in every other parking lot. But it's a point worth making that access is relatively egalitarian on the internet.