Because no-one taught them to. Just because they have access to the internet doesn't mean that they're automatically better at using it. Like how they're not automatically experts at typing or using the computer, just because they cannot remember a time before internet access was almost ubiqituous.

And since media literacy classes aren't taught as much as they used to be, they have no easy way to learn to properly critique media, and detect Misinformation. If they're left to their own devices, they don't have the skills to not fall into the Misinformation vortices when learning to critique media.

Couple that with the rise of anti-intellectualist views, and that's just a recipe for trouble. Yes, sometimes the curtains are blue because the author picked it for fun, but sometimes, the author specifically went out of their way to mention the curtains, and their colour, and there is a reason for that.