They don’t have a choice. Their infrastructure is different. For instance, Aurora integrates with IAM for authentication and has extensions to load and save to S3. Aurora writes to six different disks across three availability zones and read replicas are synchronous because they read from one of the disks that Aurora is already writing to for high availability.

You can’t get those types of features in a vendor neutral way.

The IAM stuff requires using a few hooks, at most adding minor modifications that could be upstreamed. Storage is obviously harder, but I and others are working on making that pluggable in core. Amazon's core contribution, from a few smaller things like commandline tools: 0.

Sorry, not buying it.

While not offering commits, I was under the impression that Amazon had contributed some funding. But I just went off searching for that, and can't find any evidence of this either.

Anybody know anything about them contributing money rather than code?

They've provided AWS credits, yes.

Yea, right... I don't know anything about how hard this stuff is, I'm just a postgres developer & committer, currently working on making postgres' storage pluggable.