"I can't immediately think of a reason why you'd need a publicly trusted certificate if you're pinning a specific public key"
Inter-finance systems mostly, some government. Sometimes they pin the CA issuer, sometimes IP based although with dynamic cloud IPs that is disappearing, sometimes inside a VPN, and other times just the cert issues themselves. Same service handing public users while making bidirectional API calls to other interfaces that are more locked down.
Not everyone is a monolithic copy and paste Wordpress hosting site, a new cloud native cash rich startup, or a massive Google/Amazon/Microsoft with huge teams to orchestrate everything using their own architecture and systems they developed themselves. Private PKI? Even more orchestration layers for enrollment especially in places with BYOD.
There is no point to low expiry certs anyways. If a server is hacked, the primary concern is what data were they able to exfiltrate and for how long - not that a keypair was maybe stolen to be used in a very complicated and unlikely attack to intercept some of the same data they already stole.
Your ATC comment seems to continue your theme that everyone should run a private PKI instead. Airports are full of interconnections between themselves, other airports, airlines, ground crews, satellite relays, and weather monitoring systems. So then all these parties need to do all the same actions as the public PKI - root key signing , cert issue logging, secure interface for issuing certs, develop a trust across all parties and make them install your root in all their systems ..... or, just use the public PKI services which already does that. You are just reinventing the wheel and probably will get it wrong. Maybe for some strictly backend systems, or things like server out of band management it works well, but not anything involving multiple companies.
The CAs work with large and complex business understand these complexes and voted for 2 year duration. The owners of the browsers just wanted to further their own cloud bottom lines.
"Your ATC comment seems to continue your theme that everyone should run a private PKI instead."
Not the OP you replied to, but I want to add some nuance: there's a vast solution space between using the WebPKI and rolling your own. The enterprise focused CAs have non-WebPKI CAs and CA-as-a-service offerings, both with way longer certificate lifetimes and way longer revocation periods.
If you don't need WebPKI-compatible certs (because you're not offering services to the general public) and your org cannot abide by the WebPKI rules requiring 24 hours max before revocation, you are doing something very wrong when you use the WebPKI.
I think part of the issue could be with the naming - 'public PKI'. I'd argue that doesn't really exist anymore - the nomenclature in use for some time now is 'web PKI'.
It's now ostensibly an ecosystem for use by modern, updated clients - browsers and OSs - for TLS. clientAuth will be gone from the webPKI soon, too, I hope.
It's fast becoming a more fluid, shifting ecosystem. We'll be on 90-day leaf certs very soon, shorter after that. Roots and intermediates will have much reduced lifetimes. New guidelines and regulations change things rapidly. Mass revocation events like this one.
In the ATC example - all parts of that ecosystem should be managed to the point that distributing a private root is relatively easy. It shields them from events like this. As another commenter has pointed out - running a private CA (or what might be known as an 'ecosystem CA' like we see in IoT with Matter, airlines with CertiPath, wireless with WinnForum) can be done 'as-a-service' easily, be it from a cloud vendor or CA or similar provider.
If folks continue to use the web PKI for non-web purposes, then they have to be in a position to deal with challenges like short-lifetime certs, 24-hour revoke/reissuance windows, and frequently-updated trust stores.
Most of the agreements and T&Cs for public CAs already forbid use in 'critical' systems anyway, so you're effectively agreeing to these kind of 24-hour changes from the start.
Inter-finance systems mostly, some government. Sometimes they pin the CA issuer, sometimes IP based although with dynamic cloud IPs that is disappearing, sometimes inside a VPN, and other times just the cert issues themselves. Same service handing public users while making bidirectional API calls to other interfaces that are more locked down.
Not everyone is a monolithic copy and paste Wordpress hosting site, a new cloud native cash rich startup, or a massive Google/Amazon/Microsoft with huge teams to orchestrate everything using their own architecture and systems they developed themselves. Private PKI? Even more orchestration layers for enrollment especially in places with BYOD.
There is no point to low expiry certs anyways. If a server is hacked, the primary concern is what data were they able to exfiltrate and for how long - not that a keypair was maybe stolen to be used in a very complicated and unlikely attack to intercept some of the same data they already stole.
Your ATC comment seems to continue your theme that everyone should run a private PKI instead. Airports are full of interconnections between themselves, other airports, airlines, ground crews, satellite relays, and weather monitoring systems. So then all these parties need to do all the same actions as the public PKI - root key signing , cert issue logging, secure interface for issuing certs, develop a trust across all parties and make them install your root in all their systems ..... or, just use the public PKI services which already does that. You are just reinventing the wheel and probably will get it wrong. Maybe for some strictly backend systems, or things like server out of band management it works well, but not anything involving multiple companies.
The CAs work with large and complex business understand these complexes and voted for 2 year duration. The owners of the browsers just wanted to further their own cloud bottom lines.