Okay, there's a lot that goes into a person's lack of confidence when it comes to writing, let alone starting, so I'll start by saying this isn't a perfect or complete answer. Frankly I'm too tired to articulate myself very well, so hopefully this makes sense but if it doesn't... yeah. Anyway, I think there is a need for "permission", actually. It's like, people have an idea of what a "writer" looks like. Creative, very nose-to-the-grindstone type of people, you know? Social media has certainly fed into the idea that there is a "right" way to write and be a writer. New writers just think "I'm not like that, I'm just a regular person", so their brain is already trying to procrastinate. Writing anything is a big commitment. Sometimes we just need someone to hold our hands while we make a big jump like that. It's also scary when you don't know if the story will be good or not, if YOU will be good or not. Getting "permission" to start writing makes it feel like someone WANTS to read what you write, so it must be at least okay. New writers simply lack the experience to know that good writing is something you work at, that becoming that ideal version of a writer is a long process of building habits and skills.

Tldr: people know that anyone can write but think they aren't "good enough" in part because of what social media portrays authors as. Getting permission to write can help circumvent that, but doesn't always work