Providing open-source clients does not make AWS an open ecosystem. If anything, my sense is that the overall direction of the AWS platform has been to get more and more proprietary and closed with initiatives like Lambda and Redshift that can't exist at all outside AWS. Rather than being some indication of the openness of the platform, I'd say that having open-source clients and sdks simply makes good business sense.

Once you're up and running on the AWS platform with any significant infrastructure setup, you're basically locked in for life. I hope there are counter-examples, but I'm unaware of any significant migrations off of AWS in the last few years. Some of that is due to their overall pretty high service level, but it's also incredibly hard to replicate the AWS infrastructure on your own because the tooling either doesn't exist or is immature.

I think there's a really under-served niche of startups with AWS spends of greater than $200K/year that would love to move some or most of their infra off of AWS to achieve greater cost saving or unlock different product possibilities that can come with running in a datacenter or across different cloud providers. And would be willing to pay for services and tools to fill that need. I'm finding myself in that situation now, and even though we've been careful to not get tied in to most of the managed AWS services, we're still facing lock-in due to heavy integration with cloudformation. Without a good open-source or managed service alternative to just cloudformation, we're basically faced with needing to completely re-architect our systems if we move off of AWS. And full re-architecture initiatives tend to stay near the bottom of the Devops backlog if things are working.