you can't actually learn everything on the internet.
The internet is full of beginner content, which is invaluable for getting people started. But comparatively, there is very little for people who already know a bit.
The internet incentivizes content that reaches the broadest possible audience. For this reason, there are diminished returns for creating learning content that is intended for learners at an intermediate level and beyond.
The bar for quality in terms of video editing and presentation on platforms like YouTube is also absurdly high in the current era and becomes very time-consuming to reach. This can make it even less rewarding for those that want to teach others concepts beyond the basics, especially when the chances of some monetary compensation are reduced due to The Algorithm. Usually the drive to share this kind of knowledge comes internally, which on the internet can prove to be a limitation over time.
The proliferation of only beginner content can also trick people into thinking they've already learned everything because many resources on the same topics explained are at the same level over and over, creating an exacerbated version of the Dunning-Kruger effect. Anyone with a high level of knowledge on a particular topic and has browsed a related subreddit has seen just how confidently incorrect information or bad advice on a complex subject can be delivered.
Usually if you have expert-level knowledge you want to share, you write a book or an academic paper. Otherwise, you're probably most inclined to create resources for beginners since those will reach the most people. If you have intermediate-level knowledge you want to share, most of the time the only reward you can expect is self-satisfaction. But if you're not also being compensated with money or notoriety, this can wear pretty thin over time.