First, this made me giggle because I run into that attitude all the time. "You're hosting things on a SERVER? Why would anyone do THAT? Heck, you should be putting everything in serverless and avoiding even the vague possibility that you would have to touch anything so degrading and low-class as an operating system. Systems administration? Who does that?"

In all seriousness, however, the decision (likely) has very little to do with that. They're most likely not hosting in the cloud because the current CA/Browser Forum rules around the operation of public CAs effectively don't permit cloud hosting. That's a work in progress, but for the time being, the actual CA infrastructure can't be hosted in the cloud due to security and auditability requirements.

For a service like letsencrypt, the independence factor is also a major reason for self hosting.

I can forsee letsencrypt in the future going to building their own cloud (on their own physical infrastructure), but speaking as a letsencrypt user of their free certificate program, I would lose respect and interest in their service if they went with an AWS or GCP or Azure approach.

The independence from other major players (and the ability of their team to change and move everything about their service, as needed) is one of the reasons I use letsencrypt.

Funny you mention AWS as they're one of the corporate sponsors of LE.

So long as they don't have a viable independent revenue stream they're arguably less independent than commercial CAs.

"one of" being the key point here. Let's encrypt has a huge number of sponsors (AWS being only 1 of 9 even if you only count the "platinum level" sponsors), which should allow them to maintain their independence.

https://letsencrypt.org/sponsors/

Yes it's still possible to put your own physical machines in a datacentre.

For example : https://www.scaleway.com/en/dedibox/dedirack/

I'm not sure you can say it's the cloud though.

They are not hosting their database in the cloud like Amazon or Azure because no cloud provider offers such high performances at a comparable price. Actually I'm not even sure you can get a cloud VM with that many IOs, if you don't mind the pricing.

We have a server with the hostname "cloud.example.com".

It can help if someone wants their data "in the cloud".

They are a Public CA and they must undergo a third party compliance audit to operate. The conditions are such you cannot really pass if your infra is in any of those public clouds.

Not sure if you're being sarcastic but couple of mil a year on AWS I rekon for anything similar, vs a one off 200k, not a bad saving.

And a sizable internet bill I'd assume. This puppy ain't running on Gigabit.