Anyone who thinks migrations at scale is just about “writing portable code” has never done a migration at scale.

A large corporation just migrating from everything hosted on VMs can take years.

And if you are responsible for an ETL implementation and working with AWS and have your files stored on S3 (every provider big and small has S3 compatible storage) and your data is hosted on Aurora Postgres, are you going to spend time creating a complicated ETL process or are you going to just schedule a cron job to run “select outfile into S3”?

And “most” of the services on AWS aren’t based on open source software and you still have to provision your resources using IAC and your architecture. No Terraform doesn’t give you “cloud agnosticism” any more than using Python when using AWS services.