But a massive amount of them are. Small and solo creators on Youtube or Twitch need to conform to the rules of Google and Amazon, and even medium size creators are influenced and coerced by the precedents and market trends set by the much larger corporations.
And it doesn't matter if not all content is provided by large corporations, those large corporations employ the most people, and dictate in a lot of ways, the rules of the employment market. It's due to their habits and practices that wages are artificially low and expenses are inflated for record profits.
Until corporate greed is managed properly, consumers will always struggle to have enough expendable income to pay content creators, and therefore will always be searching for free content.