Author here - as others have noted, there's a lot of benefits to a company of our size operating infrastructure on AWS vs. managing physical hardware. A couple of the highlights for managing our primary database cluster include:

- Automation - this was noted by another commenter, but with AWS we can fully automate the instance replacement procedure using autoscaling groups. On hardware failure, the relevant database is removed from its autoscaling group and we automatically start restoring a fresh instance from latest backup. This would be much more difficult if we were to manage our own hardware.

- Flexibility - we have the ability to easily change instance classes via selling/buying reservations. Some of our biggest wins historically have come from AWS releasing new instance families - we've been able to swap out the hardware for our entire cluster over a week or so, for negligible cost (often saving money in the process due to the cost per unit of hardware decreasing on new instance classes). While we could leverage the same developments in a self-managed environment, it would be more difficult, and likely more expensive due to how capital-intensive self-hosted is.

Additionally - there's a ton of value in the integration of the AWS ecosystem. We use many AWS managed services, including heavy use of RDS, Kinesis, S3, and others. For a company with a relatively small engineering team managing a large infrastructure footprint, it hasn't made financial sense yet to invest in moving to self-hosted infrastructure.