Once petabytes of data are out there in your GCP or AWS environment, "portability" will be costly due to extortionistic pricing of egress bandwidth.
Once petabytes of data are out there in your GCP or AWS environment, "portability" will be costly due to extortionistic pricing of egress bandwidth.
The portability argument boils down to saying you are not boxed in. If things get bad enough you can move. This is a big long-term advantage for businesses because it means you can correct mistakes or adjust to changing business conditions. That's what most people who run companies are really looking for.
Lots of big companies that operate extensively in AWS/Azure/GCP don't go anywhere near the managed services they offer, because they end up being a horror show in terms of scalability, functionality and troubleshootability. Depending on your risk appetite, running Kafka on Fargate/EC2 is a lot more attractive than using Kinesis (for example).
At the petabyte scale there will probably be huge cost savings to using your own private cloud on your own hardware.
And it's not mutually exclusive. I've seen companies working very cost efficiently by using dedicated hardware for 99% of the workload and AWS or GCP for any experiments where they wanted to try out new features.