Besides the security questions people have already talked about, there's a sizeable number of non-technical people for whom "www" signals "type this into a brow

Besides the security questions people have already talked about, there's a sizeable number of non-technical people for whom "www" signals "type this into a browser address bar", whereas the plain apex domain doesn't give that context because it's also in your email addresses, other subdomains etc. I don't think many people get seriously confused by it, but accessibility is for everyone and it just makes it that much easier for people to know what to do.