Because it can't be. DNS tells you who's authoritative for a name, not who's allowed to be a security boundary — and those are different questions. Whether foo.co.uk is a registrable domain or a subdomain somebody sold you is a registry business decision, and ccTLDs disagree wildly about it. Some sell second-level, some don't, some changed their mind in 2014 and grandfathered everybody. There's no field in DNS that says "the boundary is here, trust me." So the browsers gave up and maintain a text file instead, which is ugly and correct.

The part that bites harder than cookies: PSL is the closest thing the web has to an entity table. If you live on a shared suffix — anything under mooo.com, dyndns.org, the ten thousand other free subdomain hosts — every crawler and every answer engine collapses you into the parent. Your page inherits the reputation of however many hundred thousand strangers happened to register next door. That's why free-subdomain sites are functionally invisible to search and to AI answers regardless of how good the content is. It's not a quality problem, it's a missing identity boundary, and there's no content fix for it.

The whole thread is basically that tradeoff in different clothes. Free DNS, free TLS, free hosting, free subdomain — every one of those gives you something real and quietly puts you in a bucket where nobody can tell you apart from the worst neighbor in it.