Tell me about public blockchain apps that do not involve objective money or objective identity, which require strict global consensus, why they should be built on public blockchains, and why haven't they been built yet? I'll consider writing a post, when I get back to it, to explain why it does or doesn't make sense

Money and identity are key building blocked for an ecosystem

Not all apps need money and identity but if they want to be part of the ecosystem there should be something that ties it all together. In web2 it's usually SSO and permissioned APIs. An open ecosystem needs an equivalent without a trusted centralized party