I don’t understand what you mean about shareholders and pro-bono, can you elaborate? Apple advertises Apple products on Apple channels, and Apple’s shareholders love that, and it’s not “pro-bono”.

I don’t think you have the incentives correctly summarized. The incentive of businesses like Google, YouTube, TikTok, Facebook, and Instagram are to make money, and the only way they’ve figured out how to do that at scale is advertising. None of those sites had ads when they started.